Trying to cut 4 equal corners off an image

[denzjos]

There are different ways to do that and the one I use often is this plugin from Ottia Tuota :
https://www.gimp-forum.net/Thread-Roundi...odify+path
The workflow I use :
- use guides on the 4 sides of the rectangle
- make a closed path on the 4 crossings of the guides (set snap to guide : gimp menu - View / Snap to Guides)
- use the Rounding Corners plugin 
- Rounded Corners path to selection
- invert selection
- delete corners