Literally side by side? It runs into trouble with resolution, doesn't it?
I'd suggest posting a picture to the group, and then once it is in the group, if the change illustrates something interesting or useful, posting the original in the member's own photostream, and bringing it in as a link at the same size in a comment below.
Here is the before of a picture I took the other day.
Using Gimp I created 2 layers. Desaturated all colors except red on on layer and blue on another using hue and saturation. Then created a layer mask make the red layer visible. The sharpened, drop shadow, added a border, and my logo.