Continuing the discussion from When the Image IS the note:
I am very interested in reading this topic. I was very interested in this topic because my work often involves images as documents and I wanted to figure out a way to include images as much as possible while keeping the file size down in Tinderbox.
This “fill” operation is perfect for my needs, but is it not possible to do the same with an image path that is online instead of locally? 
Currently, $Fill is a File-type attribute. This reflects user requests to support images stored on their Mac’s local OS.
If you want you use internet sourced image fills, I suggest making a feature request—which should be emailed to tinderbox@eastgate.com (here is a user forum and not formal app Tech Support). As adding functionality means extra engineering (cost) it helps the developer if someone with the actual need describes it rather than simply leaving the developer to guess.
Meanwhile, if you want to make an online image accessible from your TBX file, use a URL-type attribute and make that a Displayed Attribute for your note. Clicking the globe symbol in Displayed Attributes table will open the image in a web browser. Also, you can use the attribute data in an export template such that when you preview the note the image will be displayed in the rendered page.
Hope that helps…
Thanks for the detailed description!
Yes, I agree. I was thinking it would be nice to get online, as local file paths tend to dissipate at some point.
But I have a pCloud lifetime subscription, so I will create a specific folder on pCloud and put the Fill reference images in it. That way they will not be scattered even after 10 years. 
Thanks.
A nice leverage of the existing behaviour. Dropbox users could apply the same approach, referencing the local path of the online asset.