To create a label with GIMP, do the following:

1. Open a new file with the image size supported by the label.
2. Edit the image.
3. Open the print menu and set the following configuration for your printer.
   "Image Settings" Tab -> "Adjust Page Size and Orientation"

   The supported media length for continuous tape is about 100 mm.

   Use the paper tool command to add a custom media size longer/shorter than 100 mm.
   For more information, see "Adding a custom media size for continuous tape (Linux®)".