there is already the description that is shown on top of the image when it is unlocked, you can use that ??
Viewing post in Easy Ren'Py Image and Replay Gallery comments
yes there is, edit the gallery.rpy file
in it there are two --> grid maxnumx maxnumy: <-- the first is for the images, the second is for the text adjust the --> yalign 0.1 <-- (IN THE SECOND one only) to a larger number to move it down 0.5 will be in the middle of the image and 1.0 would be the bottom