Adding DVD's to Database

[Jyroflux]

So, I finally started to add my DVD's to my blu-ray.com collection. So far a couple dozen don't appear in the database at all. Some don't show up when I scan the barcodes, of these I've found that the UPC for the entry is wrong in a few cases. I have no idea how the UPC was arrived at because I'm not able to confirm it anywhere. In those cases I just update the UPC. Sometimes it's because the UPC is missing one digit, and I update those as well.

In other cases, the entire DVD entry is just a shambles. Wrong cover art (in some cases they seem like homemade covers), wrong UPC's, very incomplete entries, etc. I'm just trying to be as accurate as possible and I don't want to hijack someone else's submission (even if it seems like a half-hearted attempt), so I create a new entry but run into trouble when the Amazon ASIN has already been wrongly attributed to another version.

Case in point, It's a Wonderful Life (Silver Screen Classics). The Amazon ASIN was used for a version that seems to have a homemade cover as I can't find a DVD release anywhere that uses that cover. And the proper cover is used in the Amazon entry.

I'm wondering:

What is the right way to add a correct entry?

and

Is it possible to add cover art at the same time as making a new entry?