Thanks for reply.
Metadata are probably not exported, but adding nodes is doing the job and its easy and fast, so I will try it. But I must do some testing, if images like this will be accepted. Thanks for help.
Well, I started few monts ago. I did some research before and it seams market is oversaturated by and prizes are low. So I decided to go with very simple images - stickman kind of images, and something on similar level of complexity. Actually draw something is easy, but to get images everywhere takes ages. So far I have about 300 images on top 10 agencies (but half of them sell almost nothing) , and few houndreds of images sold, but usual reward is $0,25 or similar, so well... its not way how to replace my usual day jobs (I'm freelancing illustrator) in next few years, maybe with some 5.000 - 10.000 images online. But thats for years. So I do it in free time between contracts, mostly because I can draw what I can. As freelancer I dont have too much of artistic freedome.