What are artifacts?

[wise]

I stumbled a few times across this word when reading about photography. The last time when I read about noise reduction programs. So, what are artifacts? And do they only occur through Jpeg compression?

 

[Big Mike]

They can occur because of jpeg compression but I'm not sure exactly how/why and if that's the only cause.

 

[Kendo]

You might want to look at this. Artifacts.

 

[wise]

Thanks Kendo. Why didn`t I think of it myself?