Okay, just want to say a few things. As someone else previously mentioned, now that Omegle has monitored video chat with an unmonitored 18+ section, I think you'll be fine. If anything, it'd be their fault for going against the rules of that lobby. Although I'm not sure how much of that would stand in a court of law. If I were you, I wouldn't worry about it.
To be honest, it'd be too much effort to actually find you just because you took a screenshot of them. As Omegle is anonymous, the only way they'd be able to track you (providing you stayed anon to them) is through the IP address. For them to do that, they'd need to know the exact time those girls spoke to you. It'd be up to their ISP to go trawling through their internet activity in an attempt to find your IP address. I'm sure that's how it would happen, may not be 100% correct but bottom line is that you're pretty safe.
In regards to the guy who thinks he's an analyst, he doesn't know shit. When you delete a file, you're not actually deleting the raw data on the hard drive, you're just deleting the link to access that data on the hard drive. That's why you can use 3rd party tools to recover data on your hard drive because it doesn't actually recover the raw files, just restores to links to access that specific data on the hard drive. You can actually recover whole partitions, not just files. Only way to truly delete is to take a hammer to it. No seriously, physical destruction to the drive is pretty much the only way. Once you destroy the platters of the hard drive, I'd say there's a 90% chance that data is gone forever. Only method of retrieving the data is through ridiculously expensive and time consuming ways and even then it's not guaranteed. Although I wouldn't do all of that just because of a screenshot