This is a "spot the difference game."

Will not say for fear of pointy objects

I've found only 3.

I only see 3 as well...

Found them all, two were harder to find so I had to cheat to find them.

how about five?

one of Momiji's bones,
the ribbon on the bloomers,
the little white stripe on Yukari
and Marisa's finger
and the red sign

After I posted, I found 2 more.

But wow, Reimu's bow pattern and Aya's wristband I never would have found.

tehSandwich said:
Found them all, two were harder to find so I had to cheat to find them.

1. The text on the arrow pointing at Suwako's chest.
2. Momiji's bones.
3. Sakuya's eye color.
4. The ribbon on Remilia's bloomers.
5. Yukari's stripes on the collar of her school uniform.
6. Aya's left wristband.
7. Marisa's right index.
8. Reimu's Donation box.
9. Marisa's hat's tip. (Cheated)
10. Pattern on Reimu's bow. (Cheated)

tehSandeich you take the cake

I still think there's a hidden one in Remilia.

11. Aya's ears.
...but you can't tell from these pictures.