Hello.
The IRC (
http://en.wikipedia.org/wiki/International_reply_coupon) is a coupon that can be exchanged for one or more postage stamps representing the minimum postage for an unregistered priority airmail letter of up to twenty grams sent to another Universal Postal Union (UPU) member country(USA, UK...)
You can buy them in the post office and they cost more than a normal stamp.
You can include the letter, of course, a photo to be signed, a SAE( an envelope with the sender's name and address on it) and the IRCs.