How to slice image as rounded object?

[toplisek]

How to slice image as rounded object?

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[Ofnuts]

Question is not too clear. Images are always rectangles. But you can have transparent pixels so that the visible part assumes any shape.

[rich2005]

A graphic image is rectangular. Not round. You can remove the background colour in the corner and introduce transparency. Your jpeg image does not support transparency. Goes like this
Add an alpha channel Layer -> Transparency -> add alpha channel
Fuzzy select the white corner (shift key to add to selection)
Grow the selection by a pixel (for those stray BG pixels)
Cut the selection
Export your graphic as a png which supports transparency.

example: https://i.imgur.com/U7cyKId.mp4

[toplisek]

I'm sorry if I was not clear. Using GIMP I try to take rounded effect from the rectangular image and paste rounded object into a white background as a new layer which will be white background.

Please find just an example and banner. It is rectangular image and a bulb. I try to do rounded effect for such object.
https://sproutsocial.com/insights/social-media-ideas/

[rich2005]

Sorry, that is even less clear Do you want to make a circular selection in one image and paste that into another Image.

That is, use the elliptical select tool, set the aspect ratio to 1:1
Make the selection
Copy it
Paste into your new image. Move to location and either anchor it or better put it to a new layer.

couple examples here: https://i.imgur.com/WP1iE6R.mp4

Or do you want to create that light bulb as a new image ?