For example, Daemon Tools Lite allows you to mount images with different parameters. So, such restrictions can be circumvented.
However, there are existence free programs To emulate ISO images that can imitate a real disk. And in the case of normal mounting, simply will not start or displays an error. Of course, some programs will recognize and use only real external disk. Today, almost any ISO file can be installed to emulate a disk, and for this you will not need any physical media. Often enough, as such, the need for physical recording on CD or DVD Disc simply no.