My understanding is that images displayed on websites need to balance quality with file size. I have been lead to believe that most screens or browsers only display 72 px/inch. This confuses me especially when there are new mobile devises that say they are high resolution or use a Retina display. Also, as soon as these devises are available there is an outpouring of upgraded apps saying they updated their graphics for the new displays. My questions are these: Do browsers or screens really only display a maximum of 72 px/in? Do these new hardware products require higher resolution images on a site to look good? What resolution is best used for a photo gallery on a site? What is the difference, if any, between the two resolutions (image and hardware pixels) I ask because I am working on putting my photographs online and would like them to be displayed at their fullest potential. Thank you.