I'm interested in doing this too but don't have much time at the moment to investigate, but I did find this thread:
https://www.construct.net/en/forum/construct-3/how-do-i-8/save-image-chosen-user-file-174429
In that example, the image is coming from a snapshot of a Drawing Canvas, but it shouldn't be too hard to swap that out for a file coming from the file chooser.
Thank you citron, i will check your advice some later and tell you is it working ;)