Window having unnecessary space

["J.Arun Mani" <J ArunMani protonmail com>]

Hello.
Im making my application for Linux systems using Python with frontend GTK+3. 
 From the pictures, you can see that whenever I attach picture, there is a lot of space created at bottom. Even it happens when I do not attach any picture, but upto a small extent only. 

But the picture is only 180×250 in size. Why does it happen? 
*Attached three screenshots.

Thank You 
J. Arun Mani

Attachment: Screenshot from 2019-01-29 23-12-45.png
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Attachment: Screenshot from 2019-01-29 23-13-03.png
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Attachment: Screenshot from 2019-01-29 23-13-28.png
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