http://www.jb51.net/article/51702.htm
https://github.com/Sybio/GifCreator
https://github.com/Sybio/GifFrameExtractor
https://github.com/Sybio/ImageWorkshop
http://phpimageworkshop.com/
http://blog.csdn.net/mingzznet/article/details/50545008 gif介绍
https://github.com/ErikvdVen/php-gif