Is there a software program that can automatically upload pics from an
external hard drive to an email in the form of an attachment?  I need
this to be fully automated without any human intervention.  The
customer would provide the email from the website.
The idea is for a website that would sell horses, cars, dogs, and etc.
 I am looking for a partner that would handle the technological
components of the business.

I'm not looking to partner but I can maybe help point you in the right direction.

(1) How do you receive the email addresses from your website?  I
assume people enter their email address in a form on your site and
that is sent to you or put into some list that you can retrieve.
(2) How do you know which picture to send to each email address, or is
it always the same picture?
(3)What program do you currently use to send email, Outlook, other? 
Will you be sending the email from an email account provided by your
Internet provider or some other account?