Editing Module:Galeria/doc (section)

=== The file parameters ===
Each file to be displayed can be spezified by one, or by two parameters. 
The chain of files starts of course with a file name; the following parameter can be the caption for the current file, or it specifies the next file name. 
When such a second parameter is the same as the first one, possibly only differing in case and space/understroke, it is used as a caption for the first parameter. 
Otherwise every second parameter seeming to be a valid file name is considered to be the next file name, and the first parameter is treated as an unpaired, single file name.

An easy solution is the specification of empty parameters for captions: it signals that the file name should also be used as the caption.