2000px on the longest side for optimum viewing online.
If you are using our Print feature, your images will need to be of a high enough resolution to produce a high quality print.
To find out what size your images should be, click here to use this helpful calculator to check the appropriate size according to your print dimensions.
If your image sizes are too small, we send you this message to let you know the paper sizes you want to sell that set of images at need larger image sizes as well.
The recommended dimensions would depend on the largest print size you are offering.