What is the native program OSX load to edit the screenshots? When creating a screenshot with Cmd+Shift+3 or Cmd+Shift+4, a smaller version of the screenshot image appears at the corner of the screen.
When clicking the image, the full-sized screenshot image pop on the screen in an annotation kind of app.

This app allows to draw, circle or outlines and it will interpolate the drawing to the closest geometrical shape.
What is this app?
Is there any way to load any image through it instead of Preview?
The editor is part of the QuickLook functionality. You can also start it by activiting QuickLook on any image (usually by pressing Space) and then clicking on the Pencil tip icon at top right.