Pasted Images - convert to jpg instead of png?

Hello,

i have a very image heavy vault and every time i paste an image into it (from my clipboard) it gets converted into .png. My vault is now over 1gb big. With .jpg it would be only around 150 mb. How can i change that for future images, i want my images to be converted into .jpg instead of .png or atleast i want them to have the same format as the source image. Most of the time that is .jpg.

My images come from google searches or other websites.

Thanks and best regards
Net

Not a direct solution to your question, but may be a useful temporary fix:

Imgur plugin for pasting images