I hope this question is on-topic... I will edit it if necessary.
I recently bought a large second hand poster-size print. It has some slight damage to the sides and a strange stain line across one side (see photos).
I would really like to restore it if possible. I suspect the background was painted with watercolours. I have some experience painting with watercolours and thought maybe I could paint the missing pieces of background as best I could on separate paper and then stick the paper onto the print. (I would try to get the new paper as level with the print as possible but I don't know how I would do that yet.)
Does anyone have any advice on whether this is a good plan?
Or if anyone has done something similar and has tips that would help?