Paper with adhesive on the back used to adhere photographs to a page on the corners. Used to adhere photos in scrapbooks and photo albums without applying adhesive directly to the photograph.
Paper or plastic triangles with adhesive on the back. Corners of photos slide into these so no adhesive is required to mount a photo.
Embellishments that are corner shaped and usually self adhesived. They either have small pockets to hold a photo in place or are purely decorative to add the corners of your picture.