If your trademark specimen has been refused due to being digitally created or altered, it means the USPTO examiner suspects the specimen has been digitally created or manipulated and doesn't show the real use of your mark with the goods/services you indicated in your trademark application.
The purpose of specimens is to prove that your goods/services labelled by the trademark are now purchasable in US commerce. A picture that shows how the trademark WOULD appear on the goods/in connection with the services cannot serve as evidence of real use.
For example, a picture showing a mock-up of a shirt bearing the trademark doesn't prove the applicant sells real shirts. If you submit a website screenshot as your specimen, it must also capture a real website the examiner can access and cannot be manipulated.