Why can't I delete the pictures from my Samsung Galaxy Avant?

Multiple times I have taken the micro sd card from the phone and inserted it in my computer to erase the photos, but my micro sd card doesn't even show all of those files. I tried using a wifi file transfer app and same thing occurs. I went through all of the apps and I haven't even signed in to my online accounts such as Google Drive, Google+, Picasa, Dropbox, Onedrive or iCloud. Where the heck are these pictures coming from? How do I stop them from automatically appearing on my phone?
Added (1). I just wanted to add that the pictures showing up are MY pictures… They aren't strange or unfamiliar…
Added (2). I thought I should add more detail…

When I click on the "Gallery" icon on this phone, several albums appear. Most of them are legitimate albums that i have created that I can also see on the micro sd card. However, there is an "Art" album and a "Thumbnail" album which do NOT appear on the micro sd card. The "Art" album shows 15,880 pictures in it. The "Thumbnail" album shows 9,642 pictures in it.

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