To take a selection sreenshot of your button on a mac — command + shift + 4
To change the default image format to JPG, here’s what you need to do.
Launch Terminal from ~/Applications/Utilities. Then enter this line of code:
defaults write com.apple.screencapture type jpg
And then this one to implement the change:
If you notice your menubar refresh itself, then you know you’ve done it right. Try it out.