When you upload your music to Score Exchange, a watermark will be automatically added over to the preview of the music displayed on the site. You can set the darkness of the overlay on the My account page.
On Score Exchange we generally show the whole score and parts on the site before a user purchases the music as people are more likely to buy something they can see first.
Making screenshots to print instead of printing legitimately is a cumbersome process, and the results are poor – not to mention illegal. The ease and quality of buying the music legitimately outweighs the time and effort required to steal your music illegitimately.