I want to build a frame (sort of like a picture frame) out of 1x4 weathered boards that's going to be 4x5 ft. The frame (without a back or anything else) will go on a wall to create an area where my kids can hang their pictures, etc. So just four boards put together with most likely a biscuit joiner. The problem I have is that I have no idea how to attach such thing to the wall. I would rather not glue because I do not want it to be permanent. Screwing into the wall would make the screws visible. Any ideas? Looking for something that puts it very close to the wall with a minimum gap.