The perspective tool looks like this in GIMP
(it may be slightly different in Photoshop, but I didn't know what software you were using.):
It allows you to correct perspective. I did a very quick edit on your picture. I simply selected a rectangle around the lower portion of the picture. I used the perspective tool to adjust his feet to about the right size, then cropped. Obviously the watermark got a little screwy, but you get the idea. I don't know why the light on his forehead changed as I didn't change the levels or curves.
