I mean that if someone sees that there is a watermark with "ofb" it wont be accepted anywhere else. The question is will this kind of watermark on a id go through their manual verification
Well they can just erase those watermarks with photoshop anyway so just like what the guy above have said, When you submit your personal documents to a third party, you are trusting your documents on them. Its really crap that bittrex didn't say any explanation on how they will store these documents.
I would avoid doing something that they didn't instructed as much as possible because it can cause you a delay on your verification or worst verification failure.
Lastly, if you have manipulated your document in anyway the verification may fail. Please make sure to submit very clear photos without any alterations.