Something else you might consider is utilizing the existing DVD covers. Find the cover you want at the
Unofficial DVD Covers post or download the archive of all the covers.
Highlight the cover only and crop. Since the DVD covers are 300 dpi this will give you a good cover image with stickers already edited off the cover. We currently have a DVD cover for every release AFAIK with hundreds . . if not thousands . . of hours spent searching for the best cover images that can be found.
I did cheat a little on my covers when good images were not available but we try to keep them as close to the original as possible. I no original can be found than we make one with available images so . . .
Doing this for Advent Rising gave me a 300 dpi cover at 700 kb I had to make it smaller to post but see attachment.