Android web cam - saving flipped image

The flipped camera issue with Android is known and simple enough to deal with display-wise, just invert the image scale or otherwise flip it.

However I'm struggling to find the solution when it comes time to SAVE a snapshot image somewhere. In my case, I'm taking the bytes and POSTing them to a partner's API. Everything works, but the image from the android side is upside down. So far I'm only seeing 2-3 possible solutions, but surely someone has managed to solve this before me:

1. Use a library like System.Drawing to apply transformations to the image -this does not work on Android - seems to be impossible due to that being a windows-only library -this works FINE in the unity editor (I'm on Windows OS as well), just not the device - so I'm taking that as Unity can deal with System.Drawing, just not on Android platforms

2. Pure C# library, no dependency on System.Drawing - I cannot find any library that does what I'm looking for (I bet it's out there I just haven't found it, hoping someone here knows...). I really don't want to hand roll something like this, but I'm prepared to if needed...

3. Build a simple web service to do this - that could easily leverage System.Drawing and return the manipulated bytes, but it is by far the least efficient approach I can think of...

Finger's crossed I'm just overlooking someone else's solution. I'm going to keep looking, if I have to write a C# library to do this by hand I'll probably look to put it on the asset store.