did this for one DD's wedding last fall - be sure to back blocks with freezer paper to make writing easier. Also I suggest you lightly pencil a 1/4" border to help people 'stay in the lines' or part of their message/picture will end up in seam.
for my other DD's summer wedding she had backing fabric as a tablecloth at gift table for guests to write on. This will be the back of a wallhanging with pictures, fabric pieces from dresses & even a piece of the johnny my husband was wearing when he arrived at rehearsal (trip to ER - motorcylce spill - long story) but happy ending :lol: :lol: