Go to the image, select options/send/via multimedia (or if viewing the
image just select send).  Image will be atached to a new multimedia
message as <image000.jpg> or whatever it is.  Select send.  Select email
address and enter the recipient's address.  Mail will be sent with the
attached image.

The mail will come from 44xxxxxxxxxx@orangemms.net, where the part
before the @ is your phone number.  Note that you have to have MMS
configured on your account and correctly set up in the phone first.  If
you can send picture messages normally then you should be fine.

I don't know whether you can attach an image to an email using the
built-in email client.