I would like to add a focal point into /mnt/overlay/dam/gui/content/assets/assetedit.html where the author can be able to focus specific image points and then I can return like .../myimage.png?focus-at=50,40
any Idea or advice would be appreciated
Can you show an example of exactly what you want to do - maybe an online demo.
In AEM 6.4, focal point is part of OOTB feature. Unfortunately, in AEM 6.3, it requires custom solution to achieve such requirements. There's a number of front-end tool that you might want to look into: