Through some odd serendipity, I stumbled across a website for a cool Gimp plugin called "Resynthesizer" that does some algorithmic texture processing and generation. The cool part is that it has some Gimp script-fu (yes, thats the proper name) to remove and synthesize portions of images. So, if you've got an image with some dust, scratches, or just some crap that you don't want to have in the picture, it will automatically remove it for you, with almost zero pain. Its really really cool. Here are some examples.
Here's the original image. We're going to be removing the tent in the middle using Resynthesizer.
In this shot, we have roughly selected the tent using the lasso.
In the next shot, we have run Script-Fu->Enhance->Smart Remove Selection, and you can see that the tent is now gone
Here is the newly patched image. If you didn't know the tent was there before, you'd never guess that it was automatically removed.
Isn't that amazing? There are all sorts of other texture-manipulation tasks that you can do, including a really cool version of "make seamless" that synthesizes a seamless texture from scratch. Its wicked.
Here's a tight crop from the full size image:
Now, we run Filters->Map->Resynthesize on it, select the tiling options, and we get the following tilable image:
Wow! Give it a try!