What does it mean that the long side of a photographic work is not less than 3000 pixels?

This is the requirement of photo resolution. That is, at least one side (length or width) of each photo must be no less than 3000 pixels.

If the photo is 4:3, then its resolution is 3000X2250, which should reach more than 6.75 million pixels.

Extended data

Photoshop image processing software, the process is as follows: file-create-establish the width and height of 600 pixels and 500 pixels (the resolution here should be the same as that of the original photo)-add photos-drag photos to a new drawing board-free transformation tool adjusts the pictures to be reduced to a complete drawing board (the scale is inconsistent, so some edge pictures will be cut off to keep the photos unchanged)-file-. 5000X3000 pixels and 600X500 pixels are just concepts of screen size. If you process it into a photo with a small size (pixels), the definition will not be bad, but it will still be very clear.