Photos not accepted

[Ziqi5E60]

Hi, I'm new in Stock. I tried to upload some photos but part of them were not accepted. It just said "during our review we found that it contains one or more technical issues, so we can't accept it into our collection." Can I know the specific reason for why it is not accepted, so i can improve. Thanks.

P.S. For example, this one is not accepted, but i got no idea. 

[Test Screen Name · Accepted solution]

The most obvious fault is the signature. Read Adobe's requirements carefully.

[Jill_C · Accepted solution]

Underexposed shadows and overexposed highlights.