find image files on a busybox machine (without using tools like file, ...)

find_images.sh

#!/bin/sh

if [ $# -eq 0 ]
  then
    echo "Usage: $0 <search_root_dir>"
    exit
fi

echo "------ start in directory: \"`pwd`/$1\""
find $1 -type f | while read fname; do
  # match on Magic number of various image files
  if hexdump -n8 "$fname" | grep -qF "0000000 5089 474e 0a0d 0a1a"; then
    echo -ne "\nPNG MATCH: \"$fname\""
  elif hexdump -n3 "$fname" | grep -qF "0000000 d8ff 00ff"; then
    echo -ne "\nJPG MATCH: \"$fname\""
  elif hexdump -n2 "$fname" | grep -qF "0000000 4d42"; then
    echo -ne "\nBMP MATCH: \"$fname\""
  else
    echo -n "."
  fi;
done
echo -e "\n------ end"