thumbnail/galery

hi!

i have a question on managing fotos:
i want the thumbnail to be a detail of the original picture. which means i save two versions of the picture: thumbnail and full size and upload them.

do you know how to set a different thumbnail from the full size picture?

also i’ d like the thumbnail to be linked to a galery. so it should show the pictures of the galery in full size (maybe in a lightbox), but no pictures of other galeries.
do you know how to do this?

thanks, grafika