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Just so we are all on the same page, you are talking about this photo in the gmail app?
Have you tried just clearing the cache for the Gmail app? Sounds like everything is OK, it's just a glitch with the Gmail app on your phone. Go into Settings >> More >> Application manager and in the 'Downloaded' tab scroll down to your Gmail app. Click on the 'Force stop' button, then click on the 'Clear cache' button. Then go back to your home screen and launch the Gmail app.
Try this, it may kick things in gear.
Settings, Accounts, Google, People Details...allow it to sync.
A long while back contact pics weren't syncing correctly and that seemed to fix it. If it does work you should be able to go back and un-sync it and still have it stay. I do recall having major issues with mine but don't any longer.
I'm seeing it in all my Google apps ... gmail, G+, Hangouts, Drive etc. What version of Android are you using?