I'm new to this GB API thing (very awesome by the way), but I don't see a way in the documentation to get a list of galleries for a game, or see what galleries an image is in, etc. Nothing to do with galleries whatsoever. Any plans for this? Did I miss it in the docs?
You can only get the default image, plus 10 of the most recent images if the resource is a game. That's probably best, actually. You really don't want to run into copyright problems with images you can't even control. You could probably claim fair use for the default image and ten screenshots. Anything more may be risking it.
If you really want to grab all the images from a gallery, maybe you could try scraping.
For these kinds of things, perhaps the API could at least provide metadata about images. Even if we can't access the images directly, knowing whether what galleries exist and how many images are in a gallery would be very useful. You could check whether a game has box art, or you could get a list of games that have galleries for platforms that the game wasn't actually released on. More valuable information could be made available if they opened up the API a bit more.
Of course, since that information's not available, getting what you want is more difficult. You could get a list of games from the API, and assume that games without images are also without box art. For games with images, you would have to fetch the actual gallery page and grep for the Box Art gallery. If there are no images in that gallery, then you can assume it is a game without box art. Unfortunately, since the image counts aren't completely reliable, you would probably want to fetch the contents of the Box Art gallery too and actually check for the presence of images. It's a bit cumbersome, but it can get you the information you want.
No idea how soon I'd get to something like this. I was just tossing around the idea in my head and playing with the API to see what's possible.