CiviMail Reports is not tracking email opens
I've experienced something similar on a few sites and it turns out the file/directory permissions are not set right. I'm not sure what causes it, but I have found that I need to recursively reset permissions after updating CiviCRM, or the tracking doesn't work, click through links don't work, you can't upload images from CiviMail, etc.

From just outside the civicrm directory, I do this and it seems to solve it:

find civicrm -type d -exec chmod 755 {} ";"

find civicrm -type f -exec chmod 644 {} ";"


The first one changes permissions on directories and the second on files. You want to avoid having anything set to 777 for sure.