2500 images flowed into iPhoto that aren't mine! What happened? Whose are they?! Do I have to go through

I tried Photos for a few days but I have used Events as a labeling mechanism and would like to continue using that as long as is possible. So I have chosen iPhoto over Photos. No animosity! No negative posting! Just a choice. I do not share an account with anyone. I do not share my Apple ID except with my own iPad. I don't know what your question about subscribing means though. I don't do anything exciting with my computer. My bookkeeping. Pictures of flowers and kids. Reading on my iPad. A very ordinary, low key computer-life.

We live in a rural area and have a small business. No one has access to my computer except me. My husband doesn't use it -- ever -- so no one else has connected a device unless some mysterious remote visitor obtained access. The pictures are labeled "Resources" and "theme-files". They are not of people but a lot of flat squares of color. They are dated from early 2000's (around 2003) until the present. When I opened iPhoto, the number of pictures I have went from over 7500 to over 10,000 lickety split. I clicked "stop import" but nothing doing -- it said I had to wait until the download was complete. So there they are -- lots and lots of squares of color and shape type imagery. Is there a way to find a "location" on the map of where they came from? Also, I quite recently did a cleaning with MacKeeper and it came up with nothing malicious there.

Other titles included such as "Brushed Metal", "Speckled Paper". We are in an art business and this looks like files from another business that is art related. This is a little bit of what people fear about remote storage -- that someone else will end up with your pictures. These are impersonal. All key words we use tend to be art related so this almost looks like a cross over from some else's art related business. This will be painful amount of deleting once I decide to do that from my standpoint, but I am a little troubled by the idea that someone else could have a load of my pictures on their computer in some sort of switcheroo.