I've seen quite a few edits like this one in the queue of late. They're almost always anonymous and trying to either link to the site that the image came from or (in this case) remove the image (which would have conflicted with both the OP and the answer). I edited the image back in, with the copyright, but I was wondering what we should do about them in general. Do we need to have a copyright statement when using diagram images from that site? Quite a few answers over the years have used them.
Content posted to SE sites are considered licensed under CC. If there is content quoted from another site, quoting and attribution is the best practice. For images, it gets more complicated since an image can be included directly from the remote source or it can be copied to SE image hosting. If that image is covered by a copyright on the remote site that doesn't allow it's usage here, then we may be required to remove it if the owner submits a DMCA take down request.
One thing we do not proactively do is attempt to remove potentially infringing material (with the exception of explicit plagiarism). We leave this up to the copyright holder to contact SE and manage that at a level above us (as described in this post).
For attribution of images (which many licenses require, including SE itself), the common markup is to use a
<sub> tag to visually separate it from the content of the answer itself.
For edits trying to remove an image, I'd recommend declining those edits. If there is an issue, the copyright holder can contact SE to have the infringing content removed that way. If instead there is an edit to replace an image with an equivalent and more favorably licensed one, I'd see that as helpful.