I have noticed that 32 character names are often used within Joplin and wonder about the reason for this. One example is the .svg files for imported icons (see my post about this here - Importing from OneNote). I have seen this pattern in other places.
Does anyone have any information on this and can explain why these files cannot be renamed without causing problems?
The 32-character string is the unique ID of the attachment or note. Everything has a unique ID. Even internal records like tags and notebook names have these IDs. It is how Joplin keeps track of everything.
For instance:
In a note you may see an image referenced as below:
The image receipt.png has been stored by Joplin using the unique reference c200fb9e741d44af9af7c1e182b47428.
If you looked in your resources folder (~/.config/joplin-desktop/resources or Windows equivalent) you would see a file called c200fb9e741d44af9af7c1e182b47428.png. That would be the attached image that had been stored in Joplin and synced to all your other clients.
If Joplin was made aware that the file was named receipt.png at the time it was attached (it wasn't pasted in) Joplin will remember that c200fb9e741d44af9af7c1e182b47428.png has a file name of receipt.png for when you use Right-click > Save as.... This also means that you can have multiple attachments called receipt.png without any file name clashes.
Because c200fb9e741d44af9af7c1e182b47428 is the unique reference Joplin uses to keep track of files and sync them, this reference should not be renamed in the resources folder or edited in a note.
If you renamed the file in the resources folder you would start getting sync errors as Joplin would no longer be able to find c200fb9e741d44af9af7c1e182b47428.png.
If you edited the reference in a note Joplin would no longer be able to find the attached file in the resources folder (as you have found).
Thanks for that description, it has certainly made things clearer.
I have another question. In the screenshot below of some test notes that I have made, there are 2 graphics.
The first is an image which I dragged and dropped in from a local folder. In the Markdown, it shows the name of the original file, "ALPS.JPG" plus the reference "ccc3e9b1d1154e9ebbcdc48d4d147215". A copy of this file has been created in my "resources" folder, as you describe.
The second is a freehand drawing which I created in Joplin with the reference "ccc3e9b1d1154e9ebbcdc48d4d147215" and the name "Freehand Drawing.svg". A copy of this drawing exists in the "resources" folder under the filename "ccc3e9b1d1154e9ebbcdc48d4d147215.svg" as expected. My question is, does the file "Freehand Drawing.svg" exist anywhere?
The reason I am asking this, is that it might help me sort out the OneNote tags as discussed in my post on this subject as linked in my original post.
According to your screenshot the unique ID for ALPS.JPG is 1534d28ba3e104a7bad500614e9fea86 not ccc3e9b1d1154e9ebbcdc48d4d147215.
So...
ALPS.JPG should be located at ~/.config/joplin-desktop/resources/1534d28ba3e104a7bad500614e9fea86.jpg
Freehand Drawing.svg should be located at ~/.config/joplin-desktop/resources/ccc3e9b1d1154e9ebbcdc48d4d147215.svg
Thanks, yes, I see my error, I did some editing in my text and obviously muddled things up!
Actually, my real question is not whether a file named "ccc3e9b1d1154e9ebbcdc48d4d147215.svg" exists, but does a file named "Freehand Drawing.svg" exist? Or is this markdown text just an indicator of an internal link within Joplin.
Thank you for your continued support 
Yes to both.
The file Freehand Drawing.svg has been attached to a note and stored by Joplin as~/.config/joplin-desktop/resources/ccc3e9b1d1154e9ebbcdc48d4d147215.svg.
ccc3e9b1d1154e9ebbcdc48d4d147215.svg IS Freehand Drawing.svg but renamed with a unique ID so that Joplin can keep track of it.
The note itself contains an internal link to that renamed file using the format .
Joplin has also stored the original filename of the renamed file ccc3e9b1d1154e9ebbcdc48d4d147215.svg, namely, Freehand Drawing.svg. (Note1)
If you right-click on the drawing in the note and select Save as... Joplin will offer to save the data from the file it is displaying - located at ~/.config/joplin-desktop/resources/ccc3e9b1d1154e9ebbcdc48d4d147215.svg - as Freehand Drawing.svg
EDIT:
(Note1) This does not refer to the filename displayed between the square brackets of the link text. The original filename is stored, I believe, in the main Joplin database. You can over-type whatever you like between the square brackets of the link and if you Right-click > Save as... on the displayed picture Joplin will still suggest Freehand Drawing.svg as the filename.
That's great! Thanks so much for the clarification.
After running a few tests, I am sure that this will help me sort out the imported OneNote tags in a more efficient manner.
I haven't had any response to my other post on this matter, so perhaps it is not something that troubles many people.
I'll mark this post as solved now, thanks again.
