UI Design Concept
Or ... why it looks the way it looks
The basic idea behind the layout is to enusre all elements stay in place,
independent of the captcha's size.
Nothing jumps around: Neither the window itself, nor the entry field, nor
the buttons.
This results in the controls needing to be placed above the captcha and
the window needing to be big enough for even the big mouse captchas.
Maybe it appears unusual, but in the end, the usability is better with
controls at fixed positions.