I figured out that the ! _Picture command (in Rhino 7) refuses to open jpg/jpeg images with a longer final name.
Example file name that Rhino does not support: 2nd-lt-jesse-van-horn-left-a-student-pilot-assigned-to-the-71st-student-squadron-goes-through-his-preflight-checks-for-the-t-6a-texan-ii-as-lt-col-daniel-heil-director-of-operations-for-the-8th-flying-training-squadron-observes-him-jan-5-on-the-fligh.jpg
Windows has a total file path limit of 260 characters. You can supposedly increase this for suitably enabled apps to 32k with a generic long file paths registry setting and a manifest file for each app (and a Policy setting in Windows Pro).
The reality is that this doesn’t work with File Explorer or at the Command Prompt. In the circumstances, expecting Rhino to handle it seems unduly optimistic.
(By moving the file to the drive root to minimise the non-file part of the path and renaming it via the command prompt you can extend the name and add the missing t at the end of flight and the longer name appears in File Explorer. But you can’t manipulate the file there by renaming it, moving it or deleting it, you have to go back to the command prompt to do that).
Yeah, after making the topic here, I tried to rename the files to make their name shorter, only to find out that Windows Explorer will not let me do that. Then I searched for a solution on Google and it recommended to check whether the Windows OS has enabled long names from the Regedit settings. It was already set that way.
I figured out that I can rename the images inside FastStone (a free image viewer) by pressing the F2 key. I will have to keep that in mind in the future when downloading images. It would be nice if a support for longer file names is added to Rhino, just like in FastStone.