GIMP is the GNU Image Manipulation Program. It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages. It is Open Source Software.
Preparation a set of pictures, their names is like to this XXXX####.xcf (XXXX is letters, and #### is digit).
Open any of them with GIMP.
Click Menu Video >> VCR Navigator..., then you get a Video Navigator window. You could set the Framerate:, which means framerate in frames/sec, default is 1, set the Timezoom:, which means to show only every N.th frame, default is 1.
You can click the PLAY button, you can preview the animation.
If the animation is good, you could click Menu Video >> Frames to Image..., then you get a window named as Frames to Image. You could set some parameters, but the most important is the Layer Basename:. In the text box, there exists something like frame_[######] (41ms). The "41ms" (ms means 0.001 second) is the intervals time between two close picture, which you could change it according to your need.
After that, you could press ok. you could get a window to save your animation, you choose your file's extension name as GIF, which makes an animation. you press ok, then set some parameters, and click ok, the computer would save your animation.
Now you could open your animation file with GIMP, then click Menu Filter >> Animation >> Playback.... You could see your animation work. Congratulations!
If there does not exist
Vedio, please download GAP plugin for GIMP.