Once you've cut the ONE triangle out, simply fold the two edges on either side to the back and you've formed a little "pocket" that will slide over the corner of your photo. BUT...before you adhere the back pieces together, you might want to dress them up just a bit.
If you want to add a decorative edge - use your edge punches, decorative scissors, or you could simply tear a tiny bit off the edge. Here, I've used some scalloped scissors to cut out part of my corner on the white piece, and I used a Martha Stewart punch on the edge of the gingham piece. One REALLY important part of this step is to make SURE that you punch/cut the side opposite the cut out notch. That's the side that will be on the top of the photo. You might also want to add a little ink to the edges or doodle on the front of the photo corner before glueing the two back edges together. I've added a little doodling to the examples below.
So...now you have the finished project. I just put the different corners on the photo so you could get an idea how they might look. Dress them up or tone them down...it really depends on the look you're going for. Once you've decided where your photo will be on the layout, then all you have to do is put some adhesive on the back of each photo corner and place it on the page. This is really a good way to add photos to a page that you might not want to put adhesive on the actual photo (especially if it is a vintage photo). I hope you enjoyed this tutorial and find it useful. If you find this to be helpful, stop by and let me know. I always enjoy hearing from you! Happy Scrapping!