A picture mount is the card insert that surrounds your artwork in the frame.
For 8 x 6 ins choice: Photo size is 7 x 5 inches with mount and photo size is 8 x 6 inches (A5) without the mount.
For 10 x 8 ins choice: Photo size is 8 x 6 inches with mount and photo size is 10 x 8 inches (A4) without the mount.
For 14.75 x 10.75 in choice: Photo size is 12 x 8 inches with mount and photo size is 14.75 x 10.75 inches (A3) without the mount.