I appreciate your reply! It does seem like I know more about the exchange than anyone else I've been able to find. Their support group isn't replying to my emails and I'm concerned about identity theft by going through the KYC process. I might end up doing that if I can determine that MixCoins is in legitimate hands, but I want to make sure my docs don't get stolen.
You could try to add a kind of watermark to your KYC images.
It doesn't need to be a digital one. But a simple piece of paper with a text along the lines "This is for KYC for mixcoins" and the current date.
You just need to make sure that one can not simply remove/cut that without it being noticeable e.g. small piece of paper across your ID.
I would notice such extra watermark shouldn't be added via Photoshop and such editors but live at shot ( for example, by keeping in hand the piece of paper with text you mentioned). They ordinary use the automated tools to check received image. Those tools are very sensitive to redaction and processed image has the risk of being rejected.