3. Making one photo the background, then arranging three others on top of it is the third way to create visual appeal with 4 photos
Shanah's cool layout will give you an idea of how well this works:
Her large photo works as a background, with an odd number of smaller photos as an accent.
Bonnie used this same sort of idea in this layout:
One of the photos is blended into the background, so your eye focuses on the grouping of three photos and registers it as an odd number of photos
4. If you use 4 photos, varying the size of the 4 photos creates a tension in the balance and fools the eye into thinking it's more or less than 4 (an odd number.)
That's what Debbie Hodge did with this layout:
And another one by Maureen:
Just by making one photo really large and the other three small, you'll be able to take advantage of the rule of odds by creating two odds for your eye to take in.