Re: # of photos...
I agree with fairygirl. Check with your PP or the mailroom. Different prisons have different rules. In TX, I could send an almost unlimited number of photos. I used to stuff a 9" x 6" envelope full of photos, and they went in with no problem.
In Virginia, though it is a different story. You are allowed to full your envelope up to 1 oz. of material. That means writing paper or photos. But only one stamp allowed, on the outside of the envelope or it might get returned.
So, check locally, to find out for sure. Sometimes that info is available on the prison web-site.
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