Da-daa, this isn't a cereal box. I know. It's a pizza box. Works the same. Don't mindlessly throw it away. ;)
Make a frame construction (maybe according to the size of your picture) and transfer it onto the fabric.
Draw an X in the middle part where your photo will be showing up.
You need to be precise when it comes to the corners.
PS: I recommend a fabric that doesn't tend to fray lots.
Trim the tips and glue them on the cardboard.
Fold over the rest of the fabric and also hotglue it.
Be careful with the edges.
Aaaand done. Actually, not, because you'll need to glue the photo on the frame and can optionally glue a piece of cardboard on the back for extra protection, let alone to add a string for hanging the frame, etc. ... yeah, I'm lazy. :D Hope you're ok with it.