Why is google docs messing up my images when I paste them and how can I fix it?

So when I paste an image into google docs, it pastes fine, but sometimes it adds small lines along the border, but only at some parts. I haven't added any border to the image or any captions. The images are only black and white. Those random lines in the top right aren't in the original image. Are there any solutions to this? I'm pasting the images from paint.net if that helps