The third image looks like a corner of the calibre component 'dialogue_warning.png'
Are you sure it's been happening for months? I wondered if it could be an MacOSX specific side-effect of the the recent deprecation of image-magik in favour of QtImage in calibre version 2.57.1. Maybe IOS version of Qtimage has a bug in resizing images. You could try reinstalling version 2.56. I say IOS specific because it's not happening on Windows.
Do you have any override images? In main GUI program (library manager) go to
Preferences->Miscellaneous and click
Open configuration directory in Finder and have a look in the /resources/images sub directory.
BR