How can I flip (mirror) a photo or image without a third party app?

[dpgriffiths]

Using JUST the stock Android Gallery app (no third party apps), on a non-rooted Android device, how can I flip a photo? When I say flip, I mean from left to right, or top to bottom. Basically, make the photo a mirrored image.

For the life of me I cannot find where this is done. I did it on my wife's phone only a few days ago and now I cannot find it. I'm losing my mind over this! She and I have the same phone, the LG G5. I'm a very experience Android user, but I cannot find info on this online and it is ridiculously frustrating!

Here's how's it was done back on Kitkat (4.4.4): http://teckfront.com/flip-image-mirror-android-4-4-4-kitkat-device/ But my wife and I are on 6.0.1, and it's as if this function is missing from Android! WTF!?!

If I'm using the "selfie" (front) camera, the LG software lets you mirror the photo you are ABOUT TO TAKE, but this seems un-intuitive because as humans we all make mistakes and we'd like to be able to flip it AFTER we've realised we want it the other way. Plus you have the option to flip it back again if you change your mind.

Please no replies with suggestions for third party apps. I am fully aware I can get this done by installing an app, but that's not the point. Either I've missed something so very simple, or Android / LG has left this function out all together.

Ugh!

 

[Mooncatt]

If they took out that option during an update, then you're out of luck and it simply can't be done with the stock gallery.

I have the LG V20 and it doesn't have a mirror option either.