Under US law you are allowed to make a digital backup of your CD/DVD/blurays for personal use, so it's perfectly fine. Not too sure about the UK (where I am from), but to be honest I couldn't really give a damn. I have a pretty big collection of DVD's and Blurays so always make a backup (ISO) of them. I also do the same for my Windows install disk. Disks get damaged so easily, so you'd be crazy not to.
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