Hi Corryne
If you want to create a Shortlist by preparing the places in a layer in a web map, such as a feature layer or spreadsheet based layer (see FAQ about that), the fields that you use to specify the image URL for the large image and the thumbnail image for each place have to point directly at the image, not a page containing an image, which is the case with your Flickr URL BlowdryLounge - Denver | Elly EDENS | Flickr . That URL won't work because it is displaying a web page, not a single image. So usually the URL will usually end in an image file extension like .jpg.
To get the direct image file URL for any public Flickr image, see these instructions in the Flickr Help:Get the URL of a Flickr photo | Yahoo Help - SLN15714
So if you follow their steps, in Flickr you'll click Download > All Sizes and get to this page for the image above:
All sizes | BlowdryLounge - Denver | Flickr - Photo Sharing!
and you can then choose the image you want to use, and right click the image that appears to get the URL you need. For example for your image I would use the Small 240 image for the thumbnail:
https://c1.staticflickr.com/5/4596/38424203824_a8f8316a1b_m.jpg
and the Medium 640 for the large image:
https://c1.staticflickr.com/5/4596/38424203824_a8f8316a1b_z.jpg
I did try the original URL you tried for the image stored in the image system you mentioned:
https://p.widencdn.net/jdwrm/blowdrylounge---Denver
This returns an image that says Preview Not Available if I open that in my web browser, so if you include that URL in a Shortlist, that's the image that the Shortlist will also display. The URL works OK: even though it doesn't end in a file extension like JPG, it still returns an image file so the Shortlist will display it correctly: It's just that the URL you are using is not displaying the image you want.
Note. Actually, are you sure you want to create your Shortlist by assembling the places in a web map layer first? Given that your images are all in Flickr now, you could just start the Shortlist Builder and import all those Flickr images directly into your Shortlist to create the places, and then add the text descriptions and organize the places into tabs interactively in the Shortlist Builder. This will automatically use the geotags for your photos in Flickr to locate the places (assuming in your Flickr privacy settings you are not hiding the EXIF data for pictures). It will also read in the captions in Flickr automatically and use them as text descriptions,. To import your Flickr images directly into Shortlist they have to be added into a public album. You'd then click Import > Flickr and type in EllyMaps to get the images. You can try this with my Flickr account (type in Rupert Essinger). My Flickr pics have captions and most of them have geotags too, so you can build a Shortlist really easily just by importing them. So it is easy to create a Shortlist from Flickr images without preparing any data beforehand.
You can also create a Shortlist by adding a point layer into a web map, such as from a feature layer or spreadsheet, create a Shortlist from that web map, and then upload Flickr images directly into those places in the Shortlist Builder, or upload images directly from your computer. This workflow doesn't require that you use the Shortlist data schema or add any URLs manually into your data. It's a handy way to make a Shortlist from your existing geodata without having to modify that data in anyway first.
The only workflow where you'd prepare your data using the Shortlist data schema, including manually entering the URLs for the images you want each place to use, is if you want to define everything in your Shortlist ahead of time so you don't need to do any interactive editing in the Shortlist Builder. With this workflow, you have the option of driving your Shortlist directly from that data in the web map, so it reflects the edits or additions you make to the data in the web map. See that FAQ I mentioned for more about that.
Rupert
