Stickies after upgrading to High Sierra

I have just upgraded my iMac to High Sierra (Version 10.13.1), and I found that two of the Stickies notes on my desktop had changed. Photos had mysteriously appeared in these two notes, with a button in the top right hand corner, and when I clicked on this I was taken to a 'Markup' window. I could find no way to remove these photos, which were obscuring some of the original text. In the end, I copied the text into new stickies, and deleted the two containing the unwanted photos. Can anyone explain what might have happened? I'd also like to know how I might have removed the photos and kept the original Stickies just as they were.