You can add up to three different slideshows to a sign.  You need to first add your slide (aka image file) to the system.  Then you need to add the slide to the slideshow on the sign.

Add a Slide to the System

• In your groups main page, click "+ Slide."

• Add a "Title" of your slide.
• Under "Slide Content" choose "Browse" to browse for the slide you want to upload.
  • Files must be less than 2 MB.
  • Allowed file types: png gif jpg jpeg.
  • Images must be larger than 1920x1080 pixels.
• Click Next.
• Enter in the "Alt Text." 
• Choose the "Image Ratio" of the image you just uploaded.
  • Take the dimension (1920x1080) and divide within each other (1920/1080)
    • 16:9 = 1.77777
    • 16:10 = 1.6
• Under "Sign Group" you can choose which areas you have rights to that can also use this image.
• Check "Share with All users" if you want anyone who has a sign in Drupal to be able to use your image.
• Click Save.

Add a Slide to a Slideshow

• Go to the sign you want to add a slide to.

• Choose the Edit Tab

• Add your slides to the appropriate slide show by clicking on "Add new slide" or "Add existing slide."
  • Add new slide:  For when you haven't added the slide (image) to the system yet.
  • Add existing slide:  For when the slide (image) is in the system already.