"Digital format" is any image format, JPEG is probably the most common but could for example be GIF, TIFF or PNG. As was said above you need to get the physical slides scanned, then whatever digital image format the scanner can save as should be useable to then make a slideshow movie
Both FotoMagico and iMovie can then accesses pictures from iPhoto or Aperture libraries (not sure about new Photos app library as I don't use it), or directly from wherever they have been saved.