Not all contracts have to be in writing (or signed) in order to be enforceable.
Under the Texas Business & Commerce Code, the following types of promises or agreements are NOT enforceable UNLESS they are in writing AND signed:
(1) a promise by an executor or administrator to answer out of his own estate;
(2) a promise by one person to answer for the debt of another;
(3) an agreement made on consideration of marriage;
(4) a contract for the sale of real estate;
(5) a lease of real estate for a term longer than 1 year;
(6) an agreement which is not to be performed within 1 year from the date of making the agreement;
(7) a promise or agreement to pay a commission for the sale of oil & gas or mineral interests/leases/royalites, etc.
(8) an agreement, promise, contract or warranty of cure relaing to medical care or results made by a physician or health care provider.
Based upon your description of the facts, it doesn't seem like you need to have a written/signed contract for your agreement to be enforceable.
So, the question then comes down to this => Did the photographer and client actually reach an agreement (regardless of whether it was reduced to writing and signed)? Said differently, was there a "meeting of the minds"? One of you may say yes, and the other may say no. And the text messages may be further evidence one way or the other. This is the type of question -- i.e. was there an "agreement" -- that may have to be settled by judge or jury.