Right, it's pretty easy, you can simply put your picture data into a variable and update the MySQL field with that info. Or, if you're using ADODB (db abstraction layer, highly recommended), use the UpdateBlob fn.
There are working code samples of this all over-- try searching here on phpbuilder in the code library, or at Zend.com. Or, hey, wasn't there an article here on phpbuilder about this just a few months ago? You'll find it in the archives.
best
Eric
http://ericmueller.org