It is common human courtesy to ask permission to take anything from you, be it your car, your money, your likeness, or an example of your work.
The 'harm in it' is not the point (that's just the old reliable 'straw man' raising its ugly mug)... and just as one can't be just a 'little bit dead', one can neither be 'a little bit robbed from'
Ask me..., and 99.9% of the time I'l say, 'No Probs'..
If one does not ask first, one is an asshole, and I would be very quick to tell one so.