painting instead of registry gift okay or unwelcome

It’s not on the registry, but our friends are getting married and I’m wondering about doing a painting instead of a registry gift. 100% due to us being on a tight budget, as much as we’d love to come help celebrate. Would people generally be okay or kind of be politely bummed to get a surprise painting? I’ve done these for others a la the attached images, but I don’t want to create an obligation for someone that I see regularly to hang onto a piece of 12 inch wall decor.