Creating GIF animation in Ubuntu
From the manual of 'convert'
The convert program is a member of the ImageMagick(1) suite of tools. Use it to convert between image formats as well as resize an image, blur, crop, despeckle, dither, draw on, flip, join, re-sample, and much more.
The above quoted paragraph is an understatement of the abilities of convert. Besides many amazing acts, Convert is capable of creating animated GIF images. For example, type the following in terminal if you want to make an animated GIF using all the PNG files in the current directory:
$ convert -delay 50 -loop 0 *.png animation.gif
Here is the animation I generated from a bunch of PNG files I previously created while playing with turtle graphics.