the only problem with responding to these is that some if not all are coded and give away the fact that your e-mail address is genuine.
Opening an e-mail with picture while online is the easiest way to tell them. The combination of pics defines you or the group that batch were sent to. Some web bot notes were the contact came from and probably puts a "yes more e-mails please" flag against that address. I never open e-mails on line and set my e-mail app to not display if I look at the folder. The bank account ones stopped 6 months ago.