Not any more difficult than mailing postcards or any document. Use a rigid envelope. Mail is usually reliable enough and this would be an "off-site backup", so

Not any more difficult than mailing postcards or any document. Use a rigid envelope. Mail is usually reliable enough and this would be an "off-site backup", so to speak. If the likelihood of losing the copy on your person is .01 and the likelihood of losing the mailed copy is .01 then the likelihood of losing your photos is .0001.