I noticed review process is faster for illustrations than photos. I wonder why DT assigns higher priority to illustrations. For instance some photos took 10 days to be reviewed (!!!!) while illustrations took one only day. This happened not only once....this is almost a rule. To me this is an incentive to produce illustrations and maybe to send photos elsewhere.
I think because photos are sold better than illustrations. Moreover, it's a little bit difficoult create a bad illustration (I'm talking about quality and execution, not ability), because of vector software like AI or inkscape.
I have no clue how their system works. I've had times where I submitted one photo, then a few days later I submitted another. The second got reviewed and approved faster then the one submitted a few days prior!
I doubt there is a priority, maybe it just happened that the photographs editors are not present vice versa. Not sure about you, but I have noticed sometimes even though images were in the status of being "Image under review", and the next few hours they were being put back to the ETR status; personally I read that as because the editor is qualified only to review photographs but not illustration images, so they skipped or passed it over, hence I believe they have two type of reviewer, professionally devoted to their field of expertise.
I had one illustration jumping the queue, it got approved while there was a waiting time of 120 hours still and got ahead of 5 photos with less waiting time. On the other hand, a whole bunch of other illustrations are waiting their turn just like my photos...
I guess there's no rule... there's just one certainty, judgement day will come!
Some other sites have lots more illustrations than photos but many are very poor standard. I am pleased that I have sold 5 photos in 6 days last week. It gives me hope to keep on improving my photography! Thanks DT.