Postage stamps from championstamp.com.
Download clip art for the text of the card, the red-squiggle design, the note for the lens, and the envelope liner (on the 3rd page).
Input details of your event into the editable file, and print onto card stock.
Print the red-squiggle design over the text by running the same card through the printer again.
Stamp our "look closer" note onto the decoding lens (send our clip art to a rubber-stamp maker, such as Stamp-Worx 2000.
Print blue envelope liner. Cut to fit the envelope. Adhere with glue stick.