The mirror will be hard to explain, because I use a German version of Gimp, but I'll try:
First of all, you mark the area you want to have in the mirror
--> After that you copy it, paste it and mirror it horizontally.
--> Move and rotate it, so that it fits to the original area
--> Fade the mirror image with the brightness option
--> Copy the original area from another image and put it over the mirror image, that is on the original area
... I hope you understand what I mean :D My English is far from being perfect
greetz
P.S.: