I use Picasa to organise my photos, even though I have Lightroom. I have other software that imports photos from a memory card and places them in folders named after the date, for example 2017/2017-01-27/IMG_1234.JPG.
When I view such a folder in Picasa I can right click on an image thumbnail and choose “Split folder here” in order to create another folder containing that image and any subsequent ones. Images prior to the selected one remain in the original folder.
I would like to find an open source program that has this feature. It’s very handy when dealing with multiple subjects taken during a single session.
Ideally I would like to be able to select a range of images to be moved into a new folder, and have the name of that folder automatically generated.
Check out Rapid Photo Downloader. While it does not have exactly what you requested, it has functionality that may get you the desired end result. It all depends on whether your different subjects from a given day have any time gaps between them. If so…
"Unique to Rapid Photo Downloader is its Timeline, which groups photos and videos based on how much time elapsed between consecutive shots. Use it to identify photos and videos taken at different periods in a single day or over consecutive days.
You can adjust the time elapsed between consecutive shots that is used to build the Timeline to match your photo and video shoots, setting it to as little as 5 minutes to as much as 24 hours."