I only see the 4th picture....Sorry for the noise, but I hope this helps...
Share link - just the photo, no album - with IMG tags around the link
Put the photo in a public album on Google Photos - share link, with IMG tags
Using the standard share link with tags:
Replace www.dropbox.com with dl.dropboxusercontent.com and delete ?dl=0 from the end:
Edit - interesting - the google links aren't even showing up as links. What the?
Me too. I'm not sure why I didn't get an empty box or anything for the first three. Inspecting the source of the page in interesting, and somewhat horrific. I think the image resizer is contributing to the problem...I only see the 4th picture....