French blogger Philippe De Jonckeere created this online chronicle of his quest to successfully transmit porn-themed mail-art using the US postal system.
The images you see on his website are original snapshots of the real envelopes that were sent from a post office in Chicago. Each of the collages were cut-and-pasted from wank mags, inserted into translucent envelopes, then sent with 25-cent American flag stamps. Link (Thanks, Jean-luc)