Well... I screencaped from zinio and I spend a time, if you can without watermarks then buy magazine and do It Yourself
I could have written that they were my own snaps and, doesn't wrong? I use those screencaped for my blog and annoys me to use my photos in my blog and do not cite the source
I screencapped things all the time. I see no reason to force someone to credit you. It was nice of you to take the time to do it but seriously the watermarks were very unnecessary. It pretty much ruined the image and the photographers great work.