I've created a map in ArcGIS online, and have added images the the popups using their URLs.
At the moment, when I embed the map and click on the feature, the text appears in the popup first, followed by the image. My question is, is it possible to change the order so that the image appears first in the pop up and then the text?\
My previous answer was not correct really. You can use the Custom popup option, which effectively allows you to configure the layout of the popup as you like. I'm not sure what I was thinking before when I answered this...
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Ok, I'm not at programmer level so will stick with the image at the bottom!
Here is a pretty good description of how to configure the pop-ups without programming: https://community.esri.com/message/622717?commentID=622717#comment-622717