As far as I see, I find phpThumb() as the best of all PHP thumbnail image generator. It has lots of thumbnail generation features. You can create thumbnail in a number of ways with phpThumb().
phpThumb() uses the GD library to create thumbnails from images (JPEG, PNG, GIF, BMP, etc) on the fly. Basic functionality is available even if GD functions are not installed (as long as ImageMagick is installed).
Features include optional resizing, cropping, watermarking, unsharp mask sharpening, rotating, caching, borders, GIF reading with/without GD support, EXIF thumbnails can be extracted and/or used for large-source support, works with any GD version, and much more.
Supported source image formats:
JPEG (via GD or ImageMagick)
PNG (via GD or ImageMagick)
GIF (via GD, ImageMagick, or phpthumb.gif.php)
BMP (via ImageMagick or phpthumb.bmp.php)
any image format ImageMagick can read
Supported output image formats:
JPEG (via GD or ImageMagick)
PNG (via GD or ImageMagick)
GIF (via GD or ImageMagick)
BMP (via ImageMagick or phpthumb.bmp.php)
ICO (via ImageMagick or phpthumb.ico.php)
Some Image processing features:
1. Source image can be a physical file on the local server, remote file over HTTP, or can be retrieved from a database.
2. GIFs are supported on all versions of GD (even if GD does not have native GIF support) thanks to the GIF Util class by Fabien Ezber, or by ImageMagick.
3. BMP source images can be used even if ImageMagick is not available.
4. HTTP thumbnail creation can be limited to the current (or other list of) domain to prevent other sites from using your server to create their thumbnails.
5. Linking to thumbnails from another domain can be prevented or watermarked.
6. Thumbnails can be cached for less server load. Mulitple sizes of any source image can be cached seperately. Thumbnails are automatically updated when (local) source image is modified.
7. Images can be rotated, either by an arbitary angle or auto-rotated to either portrait or landscape.
8. Images can be cropped, either by a specified number of pixels or by a percentage of original image.
9. A watermark image or text can be applied over the thumbnail in one of 10 positions or tiled.
10. A border or frame can be applied.
COMPLETE LIST OF FEATURES || DEMO PAGE WITH EXAMPLES || DOWNLOAD
Cheers :)