Getting a files DPI without downloading it and then looking at it in a image editor like Photoshop has been a problem since cover sites came into being.
Well I have solved this problem with new code that can check and see what the DPI is for a file on the fly.
I have now added a check to new uploads so if your file is anything but 300dpi it will fail and the gallery will not accept it and throw this error msg up:
I have added the dpi info to the gallery image display stats here:
There is a tutorial on what DPI is and how to change it here: Link To The Tutorial
It's easy to set this in Photoshop and if you are using a template that is set to 300dpi then all JPG's saved from it will be correct.