Officially speaking, you can’t view an image on a Kindle without enclosing it in a Mobipocket ebook. But there is an undocumented workaround. Sheet music is usually in static formats like GIF or PDF, so the workaround makes it easier to use legacy sheet music on a Kindle.
So here is a script to automatically handle the labor.
#!/bin/sh
#
# Given an image in the console, copy it to a mounted Kindle in such a
# way that the Kindle will include it in listings.
#
# Depends on Image Magick
IMG=$1
TITLE=$2
MOUNTPOINT=$3
if [ "$IMG" == "" -o "$TITLE" == "" -o "$MOUNTPOINT" == "" ]
then
echo 'usage: kindleizeimage [image file] [title] [Kindle mount point]'
exit
fi
if [ ! -f "$IMG" ]
then
echo "$IMG :("
exit 1
fi
if [ ! -d "$MOUNTPOINT" ]
then
echo "$MOUNTPOINT :("
exit 1
fi
tgtD="$MOUNTPOINT/pictures/$TITLE"
if [ ! -d "$tgtD" ]
then
mkdir -pv "$tgtD" || exit $!
fi
tgtF="$tgtD/"`basename "$IMG"`
convert -rotate "-90>" "$IMG" "$tgtF" || exit $!
echo "Kindle -> Alt + z"