What does this message on my computer means and how can I get rid of it?

I get a message on the upper right hand of my laptop that says my McAfee has expired. I don't even have McAfee, and I don't know where this came from, but I know they just want me to buy it. My laptop has built in virus protection already, and I have looked for this software in my files to get rid of it, but it's not even there. Can someone explain where exactly I should be looking in order to get rid if it? Or should I have someone look at it?

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file:///Users/home/Downloads/IMG_1737. PNG

This is the window I get.
What does this message on my computer means and how can I get rid of it?
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