This is a shameless plug. I had done a three part series for OSTG. Here are links to the three articles, with a brief on what each covers:
ImageMagick: A graphics wizard for the command line
covers simple image manipulations from the command line. This is a starters guide.
Advanced image editing from the command line with ImageMagick
Here I talk about the cool things like creating 2d-3d images, logos, mosaics etc.
Command-line animations using ImageMagick
This is the most recent and the last of the series. It covers creating animations from the command line.
Edit: Thanks for the link fixes TG. It's been so long since I posted any links here at LQ that I had forgotten the syntax.