Without getting way too technical you need different types of photos for different things.
When creating anything that will be printed you should be using a high resolution aka print-quality photo. This is because these are 300dpi. In simple terms, it needs to do with the quality and the fact that printers print at 300dpi.
With that being said we are also supplying you with low-resolution aka web photos. This is because monitors render at 72dpi. If you place a 300dpi image on your website it will be far too large to process and your website will run incredibly slow.