I think if it’s your first post, the site doesn’t allow you to post photos until you’ve had a certain number of posts - so keep replying! One way to tell (no need to put them in a jar) is to look at the back end of the hamster as they are just walking around. A female will be rounded at the back end. A male has a longer, more protruding oval part at the back end (effectively the top fur over their testicle area.
The photo on this site helps. It’s from underneath but you can see the difference in the shape of the back end. The male protrudes more at the back.
https://www.google.co.uk/amp/s/hamst...or-a-girl/amp/