Blank picture keeps appearing in my phone gallery, and the details about it is really strange

[Android Central Question]

My phone is a samsung and it was bought 5 months ago. Few weeks ago, the phone starts pop-up ads even when I'm not interacting with any apps, after I uninstall a PDF file viewer I downloaded from google play store the pop-ups stopped. Strange things happened after this, a blank picture (285bytes with 1x1 resolution, I can't zoom in because its too small so I'm not sure if there is any detailed picture on it) appears in my phone gallery. In the beginning I thought it was some glitch from whatsapp image but after I deleted it, it came back with the same bytes and resolution but different name, and keeps increasing. The details about the image says that the date and time image is usually one day ago, and I'm sure it wasn't there before (ex: the time says its there 7 June 12:32pm but when I open the gallery 8 June 9:30am, it wasn't there)
For more information, I once plug in my phone with my school computer but I'm sure I didn't allow the computer to access files

 

[B. Diddy]

Welcome to Android Central! Open your gallery app, select that image, and tap Info or Details, and tell us which directory it's in. That can give you an idea if it's some cached image used by an app.