> So, my question is how could I achieve the desired result for this and
> such images?
> How would do you work out similar or even more advanced cases?
There are a few good methods to use.
For cutting out a logo, sometimes using Colors>Color to Alpha with the
background color selected does the job well.
For this I would recommend using the Eraser tool, and tracing the
outline of the server. Square objects are pretty simple to do - use the
shift button to drag your Eraser tool from point A to point B.
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