So, if I take a photo and make a mosaic of it and sell the mosaic it's a violation of copyright laws?

Question

Or a mosaic of a painting. If I'm using a different medium than the original doesn't that make copyright laws in effective?

Answer 1

I am not an attorney.  Moreover, copyright laws are ridiculous and vague, and there is never a guarantee that a judge wouldn't rule in a way that ordinary people would find entirely un-cogent.

Disclaimers out of the way:

If you take a photo and use your own photo in a montage, then no it's not infringement UNLESS the thing you photographed was a registered trade mark--and there are registered trade marks in all kinds of formats, one community even trade marked a particularly attractive tree.

If you buy a painting then you own it and you may re-use it as you see fit.  If you photograph a painting, you must have its owner's permission to retain or re-use your photo.

If you photograph a person, you should get a signed permission form (find them in photojournalism textbooks)--even if you are photoing in a public place and technically it would be legal to use the photo without permission, you still should get one if possible.

Are copyright laws ineffective?  Sometimes they're far too effective.  The corporate-welfare copyright laws that have been enacted starting with the revision of 1978 have squelched creativity, hindered education, and failed to uphold the constitutional intent that originally supported such laws.

Answer 2

TR did provide a quite complete answer.

In simpler words, if you use someone else's stuff, you need their permission, no matter the format you use.