Forums and download categories both have a Cover image field on their edit screen. Drop a file on it, paste one, or click to choose.
Convoro keeps one file at one size rather than generating a set of crops. It is positioned with a focal point — a percentage down the image — instead of being cropped, so nothing is sliced off a banner.
Change the focal point when a card is cutting faces off: lower numbers keep the top of the picture. 50 is the middle and is the default.
JPEG, PNG, GIF or WebP, up to 8 MB. A wide image works better than a square one, because that is the shape it is drawn in.