And for the record, this behaviour is a normal anti-spam measure for email programs, and should ideally be left as the default IMHO. If all messages are set to auto-display linked images, then spammers can detect as soon as their linked image is downloaded from their server, and so they know they've found a live email address that is being read by a person. Best to avoid letting them know this if you can.
I have my AquaMail set to auto-display images from certain known email usernames only (it's very easy to update when you first receive a message from a new person, just tap on the prompt at the top of the message to set their email address as approved) but my default is set to not show images.
Andre