Hello,
Using
Zenphoto version 1.4.2.1 [9264] (Official Build)
Current gallery theme: zpFocus_ v1.4.2.
I have the contact form plugin enabled and I would like for visitors to be able to send me attachments, such as an image, along with their message.
I placed the following on the contact_form/form.php:

This appears on the page just fine and even lets me select a file, but when the e-mail is sent there is not an attachment (image).
I know I'm missing something. Suggestions would be greatly appreciated. Thank-you.

Since you do not mention adding any code to process that input field I would guess that you are missing something.

But also the zenphoto mailing function does not support attachements, so in addition to processing the attachement you will have to make your own mailer.