Manual signup review
Manually check each new user for missing or misleading information.
Require a minimum amount of information or photos to complete the signup process and be able to perform a thorough manual verification.
Check the uploaded images against various internet image search engines to find whether they've been stolen or not. Additionally searching for the entered texts will also detect copy-and-paste users.
Store an internal database of known scammers, and add each newly detected scammer to that database.
Search each new user against that database to find multiple signup attempts. Use the user part of the email address, the phone number, the name and surnames and the entered URLs to check each new user against the scammers database.
There are some technical methods that will allow you to identify a scammer that has tried to signup in the past and is trying to signup again with different data.
Create a requisites list for new users that makes it difficult for scammers to bypass
For example, require a minimum number of photos, a phone number, a descriptive text with a minimum length, a real name and surname, and do not allow temporal email accounts.
For companies, specially model agencies, require a fully-functional web site, a andline phone number and office address published on the site, an email address that matches the domain of the website, detailed information about the company services published on the site, some information about clients or study cases published on the site and, ideally, schedule a phone call with the company to verify their profile.
A site full of nudity will attract way more model scammers, making scam prevention more difficult.
Create a clear policy about whether your site accepts nudity, mild nudity, erotism, pornography, or none at all. Provide examples if possible.
In practice, it's impossible to create a clear internal policy to determine whether a nude photography is appropriate or not. Our recommendation is that, if you allow for nude photography, allow it only when it has a minimum technical and artistical quality. Prepare internal guidelines with examples to instruct your administrators homogeneously about those guidelines.
Provide a way for the users to report a photo when they find it's inappropriate, or it violates your TOS.
Ideally, manually check each new photo upload. If this cannot be attained, manually check only the reported photos.
Provide all users with an easy method to report any other user. Let them know their reports will be treated confidentially (and do so), and allow them to choose between some options to report, to add an additional description of the report as long as they need, and to select the private messages they've received/sent from/to that reported user to be attached to the report. Make all this fields optional.
Provide a method for your honest users to verify their identity by sending you some ID documentation.
In your TOS
You should not acquire any responsibility in regard the contents uploaded by your users since you won't ever be able to verify them all. Specify this responsibility refusal clearly in your TOS.
Specify the proper responsibilities about authorship rights, image rights, intellectual rights and industrial rights for the contents your users upload. You should let your users be completely responsible of them since checking them thoroughly is impossible.
Specify clear terms about the minimum age your users can have to use your site. Specially for models, make it so it's at least 18 years, and take into account some countries may have a minimum legal age older than 18 years. If you want to have users (specially models) under legal age, make their parents or tutors sign an authorization and send it back to you once filled and signed.
Never allow photos containing nudity of minors.
Reserve your right on the TOS to require any user to verify its identity via the method above when you find users with suspicious profiles.