16 images

If each line contains 4 images that can be ON or OFF, you have 4^2 combinations for each line.
If each line contains 16 combinations, and you have 4 lines, the total of combinations is 4^16 = 4 294 967 296 combinations

If each line contains 4 images that can be ON or OFF, you have 2^4 combinations for each line.
If each line contains 16 combinations, and you have 4 lines, the total of combinations is 16^4 = 65 536 combinations

Sorry

MJHDL:

I have a 4 x 4 grid containing 16 images that are either on or off. How many combinations are possible?

Our guest is completely correct.

I did it a little differently I just said there are 16 boxes, each can be on or off (2 possibilities each)
so the answer must by 2 ¹⁶ = 65,536
There is often more than one way to get to a correct solution.