The only definitive way to tell from a picture is the wing. The iridescence of the head is highly variable. Lessers can show both green and purple depending on the angle. In hand, the size difference is obvious, especially later in the season. The nail on the bill is another good ID method.
All but one are lessers (I think you can find the greater)
A good comparison on the wings. Greater is on the right, lesser on the left.
As you can see, lessers show a lot of green on their heads as well. From the pics you provided, along with your description of the size, I would guess
it to be a greater.