I do not have any screenshots but I will make some soon. This was done with gimp and here are the beginning/end sprites, an autocannon I made:
This
to this 
or this 
1. Open up the victim sprite in GIMP. Make sure it is not a background layer (I did this by clicking new from visible right away then deleting the original.). Duplicate it.
2. Insert a new layer filled with transparency, put this between the 2 sprite layers.
3. On the top-most layer, select all the parts of the sprite that are going to be camouflaged (i.e. the metal bits, unless it's not made of metal). Delete this and if the layer wasn't a background layer it should be filled with transparency. If not, you messed up on the first step (bummer...). This layer now only contains the background and the black outline along with any extra bits (like the ammo cases in my example).
4. On the middle layer, drag and drop a pattern (I suggest the green maple-leaf one) from the bottom-right dialogue, or the bit with brushes, pattens and gradients. You want to drag and drop a pattern into the middle transparent layer. Then set this layer to either overlay for the light, faded camo or hard light for the freshly painted one.
5. Do not merge all the layers, use the new from visible tool then delete the rest or the layer mode will disappear and everything will fall to pieces.
Not that amazing, just thought I'd give my contribution. Use different patterns for different camo effects.
I will try to get screenshots but they won't be on this for some time seeing as I go back to school on Sunday and I'm busy until then. I will get them done in school time but the chance of me being able to upload is pretty much zero. So try it for yourself! It's relatively simple.
