gimp -ib '(python-fu-mylogo-batch RUN-NONINTERACTIVE "in.jpg" "out.jpg" "Made by me" 50 "Sans" 24)(gimp-quit 1)'The language used is TinyScheme, I don't know how to use Python in this mode, but it matters very little. Any function defined in the PDB can be called including of course Python functions. Add --verbose to the command line to see the execution flow. As a side note, you can use the following command to start the PDB browser directly without going through the GIMP UI:
gimp -ib '(plug-in-dbbrowser RUN-INTERACTIVE)(gimp-quit 1)'
To make a batch mode function, add a function that opens the image, calls the main plugin function and then saves the result. Register this function also, probably under "<Image>/Tools" this time.
def mylogo_batch(infile, outfile, text, opacity, fontname, fontsize):
img = pdb.gimp_file_load(infile, infile)
pdb.python_fu_mylogo(img, text, opacity, fontname, fontsize)
pdb.gimp_image_flatten(img)
drawable = pdb.gimp_image_get_active_layer(img)
pdb.gimp_file_save(img, drawable, outfile, outfile)
pdb.gimp_image_delete(img)
The batch plugin can be invoked from the UI also, a file selection dialog will prompt the user to choose the input and output and so on.