This app demonstrates basic interactions with a dynamically-generated PNG image, which has a grid of lines spaced by 10 pixels.

With imageOutput, Shiny provides pixel coordinates. This is in contrast to plotOutput, for which Shiny provides coordinates that are scaled to the data values.

Note that depending on your browser window's width, you may see non-integer values for x or y. This is because, although the mouse cursor always has an integer-valued position, the image itself may have a non-integer position. You can see the image position in most web browsers by opening the Javascript console and running $('#image1').offset().