Do not get me wrong, but the new image has issues. It is too dark, the people merge somehow with the background making it appear like an undifferentiated mass. Probably the top section needs to be cropped away and more brightness or so may help too.
Topic on Template talk:Main page
I took a shot at making it a bit better: File:Wikimedia Hackathon Prague 2019 - 2019-05-18 - Group Picture - cropped.jpg. I cropped it down to the group of people and ran it through a filter to normalize the brightness.
Great, I personally believe this is much much better than the original version. Thanks a lot for working on this!
I suggest maybe using the other photo, the one where people aren't holding their hands in the air and thus obscuring many people's faces behind them. If easy, could you do the same brightening magic to File:Wikimedia_Hackathon_Prague_2019_-_Group_Photo_-_CLK.png? Thank you!
Took a shot -- https://www.mediawiki.org/w/index.php?title=Template:Main_page&diff=3249645&oldid=3247158 -- the thumbnail is not as pretty as I would like, so feel free to find people to try to do some more retouching.