Trigger Email Template and Reverse Email

Trigger Email Template and Reverse Email

Hay ,

Want to Create one Certificate Template and Triggered to be sent by Email When the Invoice is sent .
Certificate will be automatically populated by fields from the Invoice .( Pictures of the Service will be Emailed to Me after the work has been Completed , These Pictures need to be included with Certificate. ) 

How can we Automate this Process ?
Thank You in Advance .