I get the same results when using a virtual directory as I do when storing the images within physical folders inside the website. In the development environment using iis express and Visual Studio Pro 2015 it works great. There are approximately 200K jpg images. Sometimes when reloading the page, images that did not display the first time, will display, but I am lucky if half the images display. It seems random because the images that won't display are in the same folders as images that do display and they were all created by the same user account and process, and have nearly the same name. I have tinkered with output caching and increased most of the size limits such as maximum bandwidth (bytes/sec 4,294,967,295). I am not an iis expert so perhaps there is a way to debug the problem or check the configuration?