Here's part 1 of 3 on creating a stereogram in GIMP. This was originally posted at gimptalk.com, but I've modified the tutorial with some different screenshots which are more applicable to 3D Miracle, the stereogram creator that I'm currently using. Here's a link to the 3D Miracle site: [link]
I'm not addressing all of the nuances of the program as there are some things I don't understand about it myself. This series of tutorials is really beginner to intermediate level stuff. If you do a search on the web or here at DA, you'll see some fantastic work out there, beyond the scope of my current techniques and certainly beyone the scope of my tutorials. Here's one of the guys I watch here at DA ([link]) and Gary Priester ([link]), the man who originally inspired me and continues to Wow me with his work. Gary's tutorials are where I learned to create stereograms and gave me the inspiration to convert them over to GIMP.
I hope you enjoy this series.
As always, if I haven't been clear on a point or you need some additional information, drop me a line and I'll get back with you as soon as I can.
The tutorial is prepared in htm format. Just click the Download to Desktop button, double-click the zip file and extract both the file folder and htm file to a convenient location. Double-click the htm file to view in your browser at your leisure.