In this example, I've exported the image from GIMP to an EPS file and included the latter in the MetaPost file ttemp.mp (uploaded here as ttemp.mp.txt) using the `exteps' package:
CTAN: Package exteps
In ttemp.mp, I add a frame and the crosshairs and position the image. I could have added the text using one or more `label' commands, but I didn't do that. Running MetaPost creates the file ttemp001.eps, which I include in the TeX file ttemp.txt. Here, I add the text and have it write over the image.
I'm much better at TeX and MetaPost than I am at GIMP and I prefer to program instead of clicking through menus with a mouse, which TeX and MP make possible. For some things, the other way of working is better and it is possible to use Scheme, Perl or Python for programming within GIMP; I just have to learn how to do it. However, for typesetting purposes, TeX is certainly superior to GIMP.