Photo Quality Rating
Our Photo Quality scale performs a resolution check on your image. This is a calculation based on the number of pixels in the image versus the chosen print size. Each level of quality rating has a different benchmark for the density of pixels (or DPI). We always recommend aiming for the highest rating on the scale, if possible. Lower rating may mean that the clarity of your image could be compromised due to its resolution.
The Photo Quality rating is a great place to start with assessing your image quality for print. Other factors that are important to consider outside of the Photo Quality scale are the visual qualities of an image (unrelated to the resolution), and any cropping that had been performed. With regards to the visual qualities of an image, you will want to look out for things like focus, brightness, and contrast. These elements have to do with the capture of the photo, and would not reflect in a Photo Quality rating.
The rating can go up or down on the same image if it is cropped differently. In the act of cropping your image, you are removing pixels, and then stretching the remaining area of the image over a larger area. If you upload your image and it provides you with a certain rating, then once cropped the rating goes down, it is for this reason. If the rating is going down a lot when you crop, you may want to either choose a smaller size for the image with your desired cropping, or choose to not crop the image as much.