Last fall, Pinterest introduced "related pins," pins picked by Pinterest related to your pins and boards. The idea is that related pins will help users find new content. At this time, users can not opt out of this feature.
Related pins are based on what you have pinned and which websites you've visited recently. (This last feature utilizes cookies, but you can turn it off.) My experience is that the pins are relevant to my interests.
Here is Pinterest's example of relevant pins: "If you’ve been collecting recipes for your big holiday feast, we might
show you a related Pin for fool-proof pie crust, or the perfect
double-stuffed sweet potato."
However, I do not repin related pins. I also find that there are significantly more related pins than those from the people I am following, making it exacerbating and difficult to find the content I do want. I use Pinterest to save content for later, but that is not what Pinterest wants; Pinterest wants me to use the site more often, making it more profitable to investors. So on Pinterest's side, related pins is helpful for the business and users. Unfortunately, I'm old fashioned. If I wanted strangers on my feed, I'd add them on my own.
Here is how to identify a related pin:
You'll see that under the pin it says "RELATED PIN." This is important to look for if you have a pin from a user you don't recognize and begin to panic.
If you click the "i" you can rate the pin. For example, maybe you have a pin from Buzzfeed called "230 ways to lose weight, you dumb fat ass." (Not real!) And you are a body positive person. So you'd press the "i" for info, and rate the pin. (Pinterest: "A thumbs down will remove the recommendation from the feed and the site will learn more about what you do and don't like.")
It looks like this:
You also get info as to why the pin has been provided. I find this to be very helpful. And, truth be told, this pin is relevant to the content on my feed.
I'm sorry I have no advice on culling related pins. Related pins has been around for a few months, so it's unlikely that Pinterest will end the practice or let its users opt out. (But it would be nice if we could!)
Related Pins, Pinterest
Freshening up your home feed with related Pins, Pinterest
Pinterest Introduces Related Pins, Mashable