"Please do not steal these photos, they must be original and owned by you."

Matthew, why be coy? If you don't know, you should: owning a picture is not the same as owning copyright to a picture. What counts is copyright, not ownership of the picture. It is very unusual for models to own copyright to their pictures - and nearly as unusual for them to realize it.

To be legal, you need the pictures to be submitted with the written consent of the copyright holder - which is not what you ask for. Instead you choose language which is designed to hide the fact that copyright is at issue, and not explicitly require that written permission.

Why we are at it, what does "original" mean? In a physical sense there is no such thing as an original digital photo sent to you. In a creative sense there are very few truly original photos; most are derivative. In a legal sense it's not clear what it means, but would seem to get back to the problem above.

I will pass over the merits of your offering, which someone may think is worthwhile. But at the very least you ought to be honest and explicit about what is legally required.