Can't Delete Photos from Gallery in Android?
Here's a quick rundown of what FINALLY worked!
Do have photos/albums showing up on your android phone or tablet that you can't delete? You click on them but "delete" doesn't show as an option like your other photos? Does the album have a little Picasa emblem (rainbow color wheel) instead of a folder emblem and have a name like "Auto Backup", "Blogger Pictures", "Profile Photos"?
Get onto a DESKTOP computer (mobile app version sometimes doesn't work) > login to your google account (or login to gmail) > click picasaweb.google.com/lh/myphotos?noredirect=1 and edit away!
If you have your devices synched to your google account (which is what causes these photos to show up) then you may have photos in: this Picasa web storage; google Drive, google photos app; on your device's main storage card; your devices add-on memory card; google+; etc.
If you delete photos from here they will be wiped out EVERYWHERE: from your synced phones, tablets, computers, your BLOGGER posts, google photo app, android gallery/photo gallery app, etc. So be careful!
This is what worked when unsyncing > clear gallery cache > turn sync back on = the photos disappearing for 5 minutes and then showing back up.
Here's that trick in case you want to try it:
Settings > Application Manager > ALL > Gallery > Clear Cache.
Settings > Accounts > Google > Tap on your gmail > uncheck what you don't want synced to all your devices (Picasa Web Albums).
You can leave sync off, but then your photos won't show up on all your devices. BETTER YET: click on the link at the start of this post and edit there from a DESKTOP computer that's logged into your gmail.
Another thing that can grab and save photos/data is: Settings > Personal > Backup and reset. On all my devices this is set to save info to "Google Servers". It's actually a great feature, but all these places can be the actual location of a certain photo you want to delete, in this case a photo of a cat.
After a week of trying the cat photo is GONE from about 8 different locations/devices: including google+ which the user never signed up for but was included in the "google account". If you have gmail, then you may have all sorts of google app accounts that you never actually signed up for-they're just tacked onto your gmail now.
WARNING:
Hope this helps someone else, but remember that deleting a photo ANYWHERE in google deletes it EVERYWHERE!
SUMMARY
Eventually they might show back up. Here's another route to take: delete the photos from the FOLDER that feeds the un-deletable Picasa albums.
Get on a desktop computer > sign into google account > click picasaweb.google.com/lh/myphotos?noredirect=1 and delete the actual photos.
It will give a huge list of the places that the photo is being deleted from!
THEN go to settings > Accounts > Google > click on your gmail address which shows up > make sure "Sync Picasa Web Album" is CHECKED > click SYNC!
THEN settings > Application Manager > ALL > Gallery > clear cache.
If you don't they'll just eventually reappear. This way you can also KEEP your sync and backups going, just delete the individual photos you find annoying. This worked for a TON of my photos, but there is still one that keeps coming back, but that's better than the 305 that kept showing up! 
You ain't gonna get rid of me that easy!
When I long press that 1 photo it doesn't show the details>location like the others so I have no idea where it is coming from...and yes, it's another cat photo.
