I remember an old tread showing some pics about those tubercles on the forehead of clowns. What was the conclusion (if any), is it a sign of age....of sex...or breeding season...or ??
I just saw it on some of my 1o year old clowns (i guess) and also one these (good) pics: http://forums.loaches.com/viewtopic.php?t=11277
I tried to take some pics of mine, this is the best
As for your pic I bet if you cropped it down to just the one fish and either auto level it or manually bump the levels/contrast you could make those tubercles really stand out.