Hello everybody. I'm new in the forum. I want to post a question with a link as an example but I receive this stupid message again and again "Your post looks too spamy for a new user, please remove off-site URLs", and I don't know how to use either the web adress code. I want to learn. I need to figure out how to cut some images with polygonal shapes.

You will not be allowed to include off-site links until you have made at least 5 posts.
In the meantime, you can upload files as attachments, so download an image from the link or take a screenshot of it and upload the image as an attachment.

Welcome to Gimp Chat lucasgburgos.

All images are rectangular, those that look polygonal are still rectangular but have transparent margins and corners. So to make an image look polygonal.

- Make a polygon selection (Freehand selection in polygon mode, or using the path tool and Select>From path). If you need a regular polygon there are scripts to generate paths with such shapes.
- Add an alpha channel for transparency (Layer>Transparency>Add alpha channel)
- Select>Invert (Ctrl-I) and Edit>Clear ([delete])
- You can reduce the image to the strict minimum to encompass what is left with Image>Autocrop image
- Export in a format that supports transparency (PNG), unless you want the margins filled with a default background color.