Image Uploader API
This tutorial explains basic use of WordPress media uploader. http://wp.tutsplus.com/tutorials/creative-coding/how-to-integrate-the-wordpress-media-uploader-in-theme-and-plugin-options To add image sizes use <?php add_image_size( $name, $width, $height, $crop ); ?> Read more on this at Codex http://codex.wordpress.org/Function_Reference/add_image_size