I had to manually add:

# JPEG images
# SunOS 5.5.1 had
#
#       0       string          \377\330\377\340        JPEG file
#       0       string          \377\330\377\356        JPG file
#
# both of which turn into "JPEG image data" here.
#
0       beshort         0xffd8          JPEG image data
>6      string          JFIF            \b, JFIF standard
# HSI is Handmade Software's proprietary JPEG encoding scheme
0       string          hsi1            JPEG image data, HSI proprietary