PHP have mosts of functions available to create a image on the fly. You can use these functions to create a captcha image or a add banner on the fly.

<?php
$new_image = imagecreate( 400, 200 );
$apply_background = imagecolorallocate( $my_img, 0, 0, 255 );
$text_colour = imagecolorallocate( $new_image, 255, 255, 0 );
$line_colour = imagecolorallocate( $new_image, 128, 255, 0 );
imagestring( $new_image, 4, 30, 25, "Text Displayed in Captcha",
  $text_colour );
imagesetthickness ( $new_image, 5 );
imageline( $new_image, 30, 45, 165, 45, $line_colour );

header( "Content-type: image/jpeg" );
imagejpeg( $new_image );
imagecolordeallocate( $line_color );
imagecolordeallocate( $text_color );
imagecolordeallocate( $background );
imagedestroy( $new_image );?>

Create Image

Create image using the PHP function createimage(), function will create image with the dimensions of the image, namely its width and height in that order

Apply Colors

Next thing is to apply colors using the imagecolorallocate() function.
Colours are allocated using the imagecolorallocate() function. This function will automatically fill the background of the image with the colours you specified, and return an identifier for that particular colour. Subsequent calls to imagecolorallocate() will create a colour identifier for your colour.
imagecolorallocate() returns FALSE if the function fails for any reason.

Write Text On Image

We can write text on images using the function imagestring().
imagestring ( resource $image , int $font , int $x , int $y , string $string , int $color );
1] $image is image source
2] Font Can be 1, 2, 3, 4, 5 for built-in fonts in latin2 encoding
3] x-coordinate of the upper left corner.
4] y-coordinate of the upper left corner.
5] The string to be written.
6] A color identifier created with imagecolorallocate().

Display Image

Image is created using imagejpeg()
In this example i passed header( “Content-type: image/jpeg” ) as i want to create a jpg image.
Other functions are
1]imagepng()
2]imagegif()

Free Resources

Free individual resources which are created using the imagecolordeallocate() function and the image resource using the imagedestroy() function.

If you want to display single post page using different single post template, then wordpress in_category() function will help to create different single post template.

First thing you have to create different single post template like

single_portfolio.php
single_news.php
single_wordpress.php
single_default.php //For default single post template  for post other than above categories.

Above three files i create because i want to use different single post page template for my portfolio,news and wordpress category respectively.

You can simply create copy of your single.php file and rename it with new template and do the changes that you want for each category.

After that open your single.php file remove all code and add following code

<?php
  $post = $wp_query->post;
  if (in_category('portfolio')) {
      include(TEMPLATEPATH.'/single_portfolio.php');
  } elseif (in_category('news')) {
      include(TEMPLATEPATH.'/single_news.php');
  } elseif(in_category('wordpress')) {
      include(TEMPLATEPATH.'/single_wordpress.php');
  }
  else{
      include(TEMPLATEPATH.'/single_default.php');
  }
?>

Following code will display all the subpages of same parent page. also displays the subpages of current page if it is not a subpage.

<?php
// Get Parent of current page....
$parents_id = $wpdb->get_row("SELECT post_parent	FROM $wpdb->posts WHERE id = ".$post->ID."	AND post_type = 'page' ORDER BY menu_order", 'OBJECT');	

if($parents_id->post_parent >0) // If this page have parent
{
	// Get all the subpages of the parent page.
	$child_pages = $wpdb->get_results("SELECT *	FROM $wpdb->posts WHERE post_parent = ".$parents_id->post_parent."	AND post_type = 'page' ORDER BY menu_order", 'OBJECT');
if(count($child_pages))// If count is greater than 0
{
?>
<ul>
<li><strong><?php echo get_the_title( $parents_id->post_parent);?></strong></li>
<?php if ( $child_pages ) : foreach ( $child_pages as $pageChild ) : setup_postdata( $pageChild ); ?>
<li><a href="<?php echo $pageChild->guid; ?>" rel="bookmark" title="<?php echo $pageChild->post_title; ?>"><?php echo $pageChild->post_title; ?></a></li>
<?php endforeach; endif;?>
</ul>
<?php
}
}
else
{
	//If the current page is a top level page and it is not a subpage.
	//Get the subpages of the current page
	$child_pages = $wpdb->get_results("SELECT *	FROM $wpdb->posts WHERE post_parent = ".$post->ID."	AND post_type = 'page' ORDER BY menu_order", 'OBJECT');
	if(count($child_pages))
{
?>
<ul>
<li><strong><?php echo get_the_title( $post->ID);?></strong></li>
<?php if ( $child_pages ) : foreach ( $child_pages as $pageChild ) : setup_postdata( $pageChild ); ?>
<li><a href="<?php echo $pageChild->guid; ?>" rel="bookmark" title="<?php echo $pageChild->post_title; ?>"><?php echo $pageChild->post_title; ?></a></li>
<?php endforeach; endif;?>
</ul>
<?php
}
}
?>

Following code will retrieve all file names from a specified folder.

<?php
$filePath = "/var/www/public_html/mysite/images";/* Enter path to the folder */
$string="";
$fileCount=0;

$dir = opendir($filePath);
while ($file = readdir($dir)) {
  if (eregi("\.png",$file)) { /* Look for files with .png extension */
    $string .= "$file<br />";
    $fileCount++;
  }
}
if ($fileCount > 0) {
  echo sprintf("<h2>All Files in %s</h2><br />%s<strong>Total Files: %s</strong>",$filePath,$string,$fileCount);
}
?>

On Internet you would have come across many html forms where the value of certain fields depends on the values selected in the first select box.

So if we create this using server side script then many page loads will be needed. So if you want to create this at client side then you can create this using Jquery.

Example will be a country,state dropdown where the values in the state selectbox will depends on the value selected in the Country selectbox.

You can simply edit this script and use it as your needs.

This Error message comes when you are trying to upload image,music or video files which are not supported by wordpress.

Wordpress have some whitelist of file types which are allowed to upload, Other files are not allowed to upload due to the security reasons.

Accepted Filetypes

Images

1. .jpg
2. .jpeg
3. .png
4. .gif

For More information Read Wordpress Images

Videos

1. .mp4
2. .mov
3. .wmv
4. .avi
5. .mpg
6. .m4v

Audio

1. .mp3
2. .m4a
3. .ogg
4. .wav

Documents

1. .pdf (Portable Document Format; Adobe Acrobat)
2. .doc, .docx (Microsoft Word Document)
3. .ppt, .pptx (Microsoft PowerPoint Presentation)
4. .odt (OpenDocument Text Document)

For more information Read Wordpress Supported fietypes

If you want to display most commented post or most popular post on your blog, you can display that using following code.

Wordpress Popular Post or Most Commented Post without a Plugin

<h2>Popular Posts</h2>
<ul>
<?php $result = $wpdb->get_results("SELECT comment_count,ID,post_title FROM $wpdb->posts ORDER BY comment_count DESC LIMIT 0 , 5");
foreach ($result as $post) {
setup_postdata($post);
$postid = $post->ID;
$title = $post->post_title;
$commentcount = $post->comment_count;
if ($commentcount != 0) { ?>
<li><a href="<?php echo get_permalink($postid); ?>" title="<?php echo $title ?>">

<?php echo $title ?></a> {<?php echo $commentcount ?>}</li>
<?php } } ?>
</ul>

This is excellent php function which can be used to get Width,Height,Type of a Image using PHP. for more information read PHP.net

list($width, $height, $type, $attr) = getimagesize("image_name.jpg");

echo "Image Properties";
echo "Width " .$width;
echo "<br/>";
echo "Height " .$height;
echo "<br/>";
echo "Type " .$type;
echo "<br/>";
echo "Attribute " .$attr;

Type of the image

1 = GIF 5 = PSD 9 = JPC 13 = SWC 2 = JPG 6 = BMP 10 = JP2 14 = IFF 3 = PNG 7 = TIFF(intel byte order) 11 = JPX 15 = WBMP 4 = SWF 8 = TIFF(motorola byte order) 12 = JB2 16 = XBM

JQuery is a fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development. jQuery is designed to change the way that you write JavaScript.

Below you will find most powerful, the most creative and most versatile of jQuery plugins and tutorials built using jQuery.

1] Jquery InnerFade

InnerFade is a small plugin for the jQuery-JavaScript-Library. It’s designed to fade you any element inside a container in and out.
These elements could be anything you want, e.g. images, list-items, divs. Simply produce your own slideshow for your portfolio or advertisings. Create a newsticker or do an animation.

2] Galleriffic

Galleriffic is a jQuery plugin that provides a rich, post-back free experience optimized to handle high volumes of photos while conserving bandwidth.

3] Popeye – an inline lightbox alternative

Popeye generates an inline image gallery from an unordered list of images. The gallery features clever inline image enlargement, i.e. the enlarged image stretches out over the site content without adding a visual overlay of the whole site.

4] ShowCase

This plugin builds an autoscrolling, navigable image gallery, perfect to do a modern showcase in a portfolio web site.

5] PictureSlides

PictureSlides is a plugin for jQuery, and it is a highly customizable JavaScript-based way to easily turn your images into a collection viewable as a slideshow, and with fading effects

6] Jquery ImageSwitch

Jquery ImageSwitch is easy-to-use, simple and fast plug-in to create effect when you switch between images.

7] S3Slider

The s3Slider jQuery plugin is made by example of jd`s smooth slide show script.

8] Gallery View

GalleryView aims to provide jQuery users with a flexible, attractive content gallery that is both easy to implement and a snap to customize.

9] Galleria

Galleria is a javascript image gallery written in jQuery. It loads the images one by one from an unordered list and displays thumbnails when each image is loaded.

10] CrossSlide

CrossSlide is a jQuery plugin that implements in Javascript some common slide-show animations, traditionally only available to the web developer via Adobe Flash™ or other proprietary plugins.

11] A Simple jQuery Slideshow

This is a nice tutorial to create simple Jquery slideshow.

12] Smooth Div Scroll

Smooth Div Scroll is a jQuery plugin that scrolls content horizontally left or right. Apart from many of the other scrolling plugins that have been written for jQuery, Smooth Div Scroll does not limit the scroling to distinct steps.

13] Simple Controls Gallery

Simple Controls Gallery rotates and displays an image by fading it into view over the previous one, with navigation controls that pop up when the mouse rolls over the Gallery.

14] Sliding Image Gallery

The idea behind this plug-in is to display a varying number of images in an attractive and easy to use manner.

15] Flickr Photo Gallery

flickrGallery is an open-source photo gallery for jQuery that allows you to dynamically pull images from a photoset in Flickr.

16] Pikachoose

Pikachoose is a lightweight Jquery plugin that allows easy presentation of photos with options for slideshows, navigation buttons, and auto play.

17] EOGallery

EOGallery is a web animated slideshow gallery maid with jQuery. It only uses basic jQuery functions and Cody Lindley’s Thickbox to display larger pictures.

18] Full Screen Image Gallery Jquery and Flickr

full screen image gallery that automatically scales the image with kept aspect ratio to fill the browser background.

19] jQuery morphing gallery

Image grids that smoothly scale at the simple drag of a slider are no longer confined to desktop apps like iPhoto or Picasa.

20] Simple JQuery Image Slide Show with Semi-Transparent Caption

simple image slide show with a semi-transparent caption with jQuery. This example is suitable to display news headlines, or a image slide show in your website frontpage.

21] Slick and Accessible Slideshow Using jQuery

Create a usable and web accessible slideshow widget for your site using HTML, CSS, and JavaScript (jQuery).

22] Ultimate Fade-in slideshow (v2.1)

This is a robust, cross browser fade in slideshow script that incorporates some of your most requested features all rolled into one.

23] AD Gallery, gallery plugin for jQuery

A highly customizable gallery/showcase plugin for jQuery.

24] Jquery Panel Gallery Plugin 1.1

25] SlideViewerPro 1.0

slideViewerPro is a fully customizable jQuery image gallery engine wich allows to create outstanding sliding image galleries for your projects and/or interactive galleries within blog posts.

26] Easy Image Preview with jQuery

Some Other Slideshow Scripts

Animated JavaScript Slideshow

When you want to display all the child pages title and excerpt of current parent page then you can display by adding following code in your page template file

<?php
$child_pages = $wpdb->get_results("SELECT *	FROM $wpdb->posts WHERE post_parent = ".$post->ID."	AND post_type = 'page' ORDER BY menu_order", 'OBJECT');	?>
<?php if ( $child_pages ) : foreach ( $child_pages as $pageChild ) : setup_postdata( $pageChild ); ?>
<h2 class="subpagetitle"><a href="<?php echo $pageChild->guid; ?>" rel="bookmark" title="<?php echo $pageChild->post_title; ?>"><?php echo $pageChild->post_title; ?></a></h2>
<?php the_excerpt();?>
<?php endforeach; endif;
?>

If you don’t want to display child pages on every page then you can use Wordpress Conditional Tags.