This is a BTMail based problem, probably linked to the rather underwhelming "improved " service their recent changes offered, it is not linked to the browser used. The system has been written to assume any image attached to an email may have malware etc attached, hence the note and removal of secure lock icon when the email is opened. There is a work around by amending the "block image" option in settings, then it's OK but clunky.
While you can then amend an individual email with images (those on your contact list should (?) show images with no problem) by clinking on "show images" in the mail header, there doesn't seem to be a reverse switch, yet more poorly developed software.
This will be the 3rd or 4th compromise I've had to make to work with the new email system to keep it roughly in line with the facilities I had when they used the Yahoo framework, I could bleat about the Calendar changes, I have muttered to BT but to no avail, apparently the systems guys decide, the consumer is just a tiresome distraction.
