In article ,
ospam says...
BIG SNIPS

In order for a contract to be formed each party must give
something of value to the other, it must be an exchange. If a clause of

the contract confers reuse rights to the photographer, something of
value must also be transferred to the customer. It could be anything, a

free 8x10, a discount on the session cost, even a single buck politely
handed over. Whatever it is, it has to be clear and explicit.

Where in copyright law or elsewhere in the law does it state that a contract
must be a bilateral agreement in order to be legally enforcable?

It's not copyright law, it's contract law.

Isn't a unilateral contract also enforcable?

A unilateral "contract" is not a contract and isn't enforceable because
it doesn't exist.

WHy does something have to be in exchange
for something else.

Because that's the law.

A contract is merely an agreement, that's all, whether
something is exchanged is besides the point - though few people will sign
things without getting something in return, those that would sign a contract
(ie. a modle release) (perhaps a friend or a relative would be more likely to
sign w/o getting somthing in return than a total stranger or a client) have
given their right and permission for their likeness to be used whether there is
something in exchange (valuable consideration) or not.

Simply not true. A mere agreement is not a contract and is generally not
enforceable. There are exceptions for things like if "reliance" on the
agreement can be demonstrated, but that's starting to stray.

It is till a legal
agreement I beleive the same may apply for a witness, that a witness is not
needed, despite what one may have heard otherwise to make a contract "legal."

No witness is required for a contract to be formed, but they come in
darn handy in verbal contracts and other dodgy legal situations.

Mark