I would like to take an image and create ripple effects on it, similar to the (poor quality) background in this YouTube video. Is there any free software out there for this purpose? Or ways to do it in GIMP? Or, possibly, an idea of what would need to be done using a programming language?
If you need just static image, then yes its possible to do in GIMP using a displacement map. You would make black and white picture of the ripple you want an then use it as displacement map on your image in GIMP.
If you need to make movie (like the video you posted) then you need some video editing software with effects. Probably the best open-source solution is Jahshaka but its more involved - i would refer to tutorials on their site. Simpler free solution might be trial version of Adobe After Effects but that also might be overkill.
If you want to use programming language, i would suggest Processing - processing.org
Btw sorry i can't post more than 2 links.