There used to be a way to list products you used from the store in an image. I can't seem to figure out how you do that anymore. I would love to give credit to the vendor's who's products I support and use. Can one still do that and how?

On the "Upload Art" page, the second main section is titled "production credits". Type in the username of the vendor whose product you want to credit, then there will be a dropdown list of all that vendor's current products for you to select the right one.

If it's not a current product then you'll have to credit in the comments section.