I've always wished I could make mosaics but I never had the materials to do them so I thought that I could still do whatever I wanted recycling what I don't need anymore.
Just like with all mosaics, you need a lot of patience, but the result is great and the feeling of satisfaction you get looking at it is worth the time and patience, believe me!
Take a piece of cardboard and draw a rectangle: you must consider how big the picture you will frame is. Mine is 13x18 cm (5.11 x 7.1 inches) so, adding 4 cm (1.57 inches) on every side for the frame, my rectangle is 21x26 cm (8.28 x 10.23 inches).
Cut the rectangle and make another identical one so you will have 2, one for the front frame and one for the back.
Take the first rectangle and draw a 13x18 one in the center counting 4 cm from each side. Depending how big your picture will be, your measures will be bigger/smaller. Once you have traced this last rectangle, cut it out and you will finally have your frame!