Originally Posted by luket
Well, that's one of the problems. If I drag 3 files, there is no complaint, but only one is uploaded.
If I could drag all allowed, (or even more than one,) I would be quite happy.

The wording of the uploader suggests that only 1 be allowed at a time. This is by design, since this is a message forum file attachment manager, rather an specifically a photo gallery software package. UBB.threads assumes a minimum server requirement for processing/compressing what would be multiple large images at the same time while expecting equal performance for the other forum users on server, and possibly other websites, especially on shared servers.

Originally Posted by luket
I have thousands of pictures that want to upload to the server to appear in ‘picture of the day’. The only way to do this is by uploading them one-by-one.
Better would be a place on the server where I could just dump my thousand pictures and tell the system where they are (for my picture of the day.)

Uploading thousands of images to a single post? You probably would get the exact expereince youre looking for if you used a photo gallery software for managing your gallery of photos, instead of using a message forum software which was designed to manage typed messages. Thousands of images attached to a single post would not be user friendly to the post attachment viewer. A modern photo gallery software package should be able to allow your users to comment on single photos, or even a single gallery folder of photos.

Have a look at Piwigo Gallery software for managing your photo collection online
https://piwigo.org/

with 3rd-party, unsupported code -
As an idea which you could expand upon, is to use Piwigo Gallery to manage your photos, and setup an RSS feed which pulls a random image from one of your defined galleries each day. Then use the UBB.threads RSS Topic Creator to grab that RSS feed and insert it in to your forum as a new post in a dedicated forum category.
UBB.threads RSS Topic Creator @ UBBDev
https://ubbdev.com/forums/ubbthreads.php/topics/323588/1.html

an easier route -
You could also just use the 3rd-party photo gallery's "embed random image" plugin to create a UBB.threads Custom Portal Island. Most gallery software provides a block of php code specifically for this perpose.