@yogi108 : I am trying to proof my concept using widget alone, need some time. Resize me pro for free is just pure coincidence
You need to enable edit image from other app in the setting, in order to to crop manually after opening from Automagic.
Finding the "extra" passed is one of the challenge. I usually use intent intercept (can be downloaded from F-Droid, if you can't find it in playstore), if the app have the export/share intent or receive it. But if the activity is started background, you can take a peek of its action using logcat. Which I have done using my logcat flow, filter for ActivityManager. However, we still can't see the extra, which I am still trying to find the way. So far, unless the dev provide the documentation for it, it is quite difficult to know the detail. You can decompile the apk, but it is very difficult to search for it.
@BoBo : Most don't. If they open up, usually thru broadcast or activity, not from command line. Have to ask the dev for it. Usually they will provide a good documentation if they have decided to open up their function.