It seems that the descriptions of all existing images in the gallery get erased when a new picture is uploaded. How can I fix this?

It's strange. I can't reproduce this problem. Can you try the following demo:

 

 

 

 

So if I drop a file in the album, how does it get added to the gallery without doing a batch build?

Jedon,

 

Please use the upload button to add the new images to the album.

 

 

But I don't want to use the upload button, because then I can not programatically insert images into the gallery. What is the use of a simple file based gallery if you have to have a person manually upload images?  I would be satisfied to be able to manually call the generate thumbnail routines on the object from my C# code.