Using the picture that someone else took without that person's permission is an infringement of copyright, but I can't see how that person would suffer and damage by such use if the picture was a private photo not being marketed. So even if the copyright owner sued you, the worst that could happen on that score would be statutory damages, which will depend on the jurisdiction. In the US the potential damages cover a wide range, and the judge has discretion on where to set them. And of course, the person has to know you used the photo to sue. In the US, if the copyright wasn't registered, statutory damages may not be available.
If the person whose image you use is not using his or her image to market anything, and you are not going to use it to market anything, there should be no issue of personality rights here.
You will be lying, and violating the site's TOS (presumably), but unless you gain (or intend to gain) something of value, or deprive your victim of something of value, it isn't legally fraud, but rather a hoax. The site owner might be able to sue you for contract violation over the TOS issue. But I don't see any criminal proceedings over this.
Depending on your jurisdiction, you might be violating some law about Unauthorized Access to a Computer System. That may be a crime, or only a tort that the system owner can pursue, depending on your local laws.
Still if this comes out (and it is surprising how often such deceptions do come out) it will quite likely harm your reputation, possibly significantly, and it might lead to legal problems. Is it really worth it?
In an case, I am not a lawyer, and I am definitely not your lawyer. If you do this, don't do it on the basis of this post, which is made for educational purposes only.