Hi,

I looked up the Forge but the only component I found was mobile-only and looked discontinued. 

I think you'd have to implement this yourself with Javascript and the canvas element. You can convert a canvas to a PNG file as well as draw over an existing image. Combining those two should be enough for what you need.

You can use this forge component

https://www.outsystems.com/forge/component-overview/4611/drawerjs

and configure the 

drawerJsConfig.js on the Resources and add this 

'Image'

here's the link of the documentation : https://github.com/carstenschaefer/DrawerJs/wiki/Image

then you'll be able to add Image through the component and mark the image. :)