I dont know about the rock image as I would have to look at your folder structure, but I do know about the "folder.jpg" part, its because you have windows set to hide filename extensions for know file types (google it) its just a tick box you need to uncheck in your folder options. so when you just have "folder" and it works its because the ".jpg" part is hidden, so when you type "folder.jpg" you are actually getting "folder.jpg.jpg" so it dont work.