This seems somewhat simple to make but i don't know how to split a photo up into fours or trios -- then angle the photos. It looks like the end of each picture at the angle has a blended colorless stroke? how do i complete that?
You can use the Paint Bucket Tool to fill it with the Foreground color..........which should be white.........hit D on you keyboard.
If the foreground color is white, you can also hit Option/Alt + Delete to fill with foreground color. Com/Cntrl + Delete will fill it with the background color. Hitting X on the keyboard will alternate the foreground and background colors.
Or you can use EDIT > FILL (shift + Delete) and choose white.