@trustinglife: Most people, when they upload an avatar photo to Fluther, use an image larger than the 40×40 thumbnail displayed here.
So, what Fluther does is it makes a copy of the photo you uploaded and inserts the string “_thumb” in the filename.
For example, your original photo was a good size. I was able to get to it by:
1. right-clicking on your thumbnail image and getting the image address. Note the “_thumb” in the filename at the end.
2. Copy that url, remove the “_thumb” portion, and input the resulting url into the browser (or your Fluther textile markup).
3. Voila! Big pic.
Remember, it only works for those pics that were large to begin with. My avatar has nowhere to go as I uploaded something close to the Fluther thumbnail size to begin with. You’d hafta get crazy with some dedicated software, like @deezer suggests, to get my avatar any larger.