So it looks like the raw URLs you posted are:
https://imgur.com/a/tKQplIg
https://imgur.com/TznlHJF
https://www.dropbox.com/s/5kqlet57mzn8rv8/IMG_4637.jpeg?dl=0
Imgur
The first one links to the Imgur album whereas we need a raw link directly to the image. Similarly, the second link points to an imgur webpage that is displaying the image. So following the tips in the How To: Add photos to a dashboard post, if we open up that Imgur page and get the link directly to the image, we would get the following URL which should work:
https://i.imgur.com/L4W3EOC.jpeg
Dropbox
And for the Dropbox one, it’s also linking to a webpage which displays the image. So if we change the dl=0 to raw=1 it should work too:
https://www.dropbox.com/s/5kqlet57mzn8rv8/IMG_4637.jpeg?raw=1