How can I create an image submission form which accepts high quality photos?

That's easy, when you add an upload field to your form. Set a minimum file size like 1MB (since most high quality image has bigger file size), normally smaller file size means low resolution image.

1. To add minimum file size limit, you have to open the file upload field properties.

2. Then set the minimum file size limit:

You can also play with the other configurations like the allowed file extensions. You can also enable multiple file upload.