This photographer was the author and copyright owner of the photos once the photos were created, and if he gave them to you, he presumably did so thinking you understood that he owned them, they're not free, and he expects to be paid for them if you want to use them. The photographer isn't the one who needs anything signed to establish his ownership, quite the opposite, you're the one that needs something in writing saying you have some right to use them. You're committing copyright infringement, and should either take the photos down off the site and don't use them, or make a deal with the photos' owner.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
The below does not constitute legal advice, does not form an attorney-client relationship, and should not be relied upon to take or refrain from taking any action.
I take it that you're a model. A photographer took pictures of you. He or she gave you copies which you then published. As a result, you signed a contract with a modeling agency. And now you want to know if you can continue to use the pictures? Does "yes" sound even remotely right?
No. The photographer owns the pictures (the copyright and probably the hard or digital copies as well). You cannot use them without the photographer's consent.
I disagree with Ms Koslyn's answer. Whether the photog had a copyright interest is not at issue. If the photog gave the images to you with NO directives as to the limit of their use, he may not subsequently seek to impose a contract nor assert his copyright privs.
That being said, I wonder whether you have left out some of the discussion with the photog in your question. Therefore any answers given you in this forum MUST be taken limited to the simple set of facts you have presented, ANY new or different facts WILL LIKELY CHANGE THE OUTCOME.
At any rate, it matters not what the law may determine. If the photog decides that he needs to sue you to protect what he views as his property (i.e. his work), you will have to bear the cost of that suit in order to protect your interests. Therefore, it may really be in your best economic interest to take the photos down, if only to save yourself the possibility of his seeking legal recourse.