I have one person in my addressbook with the given name "Oliver" and a photo attached. Regularly when a new mail arrives from an entirely different person, which only shares the given name "Oliver" with the contact, the photo of the contact is shown. The mail sender is not in the address book, nor has he the same last name, email address localpart, or email domain. If I look at the mail in KMail the wrong photo is not displayed. Reproducible: Always
I've observed this too with kmail/kaddressbook 4.14.10 under openSUSE 13.2 and lap 42.1. Right now I've upgraded the whole kdepim/kmail/kaddressbook stuff to kdepim-15.12.0-6.1 and no contact photos from my address books are shown anymore at all, not even in the header of received emails. This is also a possible way to fix this bug. :-(
This bug has never been confirmed for a KDE PIM version that is based on KDE Frameworks, except possibly a Technology Preview version 5.0.x. Those Framework-based versions differ significantly from the old 4.x series. Therefore, I plan to close it in around two or three months. In the meantime, it is set to WAITINGFORINFO to give reporters the opportunity to check if it is still valid. As soon as someone confirms it for a recent version (at least 5.1, ideally even more recent), I'll gladly reopen it. Please understand that we lack the manpower to triage bugs reported for versions almost two years beyond their end of life.
Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.1 aka 15.12; preferably much more recent), please open a new one unless it already exists. Thank you for all your input.