5K Retina mac developed this in a few months.

[mustu]

Hello Okay so my 5K Retina mac developed this, dark mark behind the screen. Would anyone have an Idea as you what it is?

 

[Samuelsan2001]

No idea, but if it's only a few months old it's under warranty so get apple to fix it.

 

[cbrand493]

Looks like something actually stuck to the screen than behind the screen. Have you tried cleaning it?

 

[ucfgrad93]

No idea, but if it's only a few months old it's under warranty so get apple to fix it.

Agreed, if you can't remove it then take it to the Apple Store for a replacement.

 

[Aspekt]

Like many have suggested, if you aren't able to clean it, and the fact that it is only few months old, simply make a appointment with the store and take it in for a check.

Since we can't be sure if they will replace the whole computer or just the screen, you should definitely backup everything before you bring it in.

 

[redheeler]

It looks like something has found its way into the screen, which can happen. I agree with the other posters, since your iMac is still under warranty take it to the Apple Store. It might help to bring that photo as well.