Use cursor to draw the capture area

[AnderRasoVazquez]

Describe the solution you'd like
Click and hold to draw a rectangle of the window. That rectangle would be the preview.

Additional context
i.e. elementary OS captures the screen drawing the area with the mouse.

[medenagan]

I've seen it in Elementary OS, it's definitely a cool feature, hope to add a similar feature

[padok]

I would even go one step further and suggest an auto-crop button that removes black, white and transparent borders.