Image MIME types tend to have values like 'image/tiff' and 'image/gif'. My quick explorations suggest that the correct MIME type for a .bmp file is 'image/bmp'. (Natch!)

You also should have a Content-length: line in your http header. Then print a blank line: 'print "\n";' to end the http header.

Then do a binmode STDOUT; and spit out the data that makes up the image.

You close the image by ending the script.

# assumes image data is in $image
my $size = length $image;
print "MIME-version: 1.0\n";
print "Content-type: image/bmp\n";
print "Content-length: $size\n";
print "\n";
binmode STDOUT;
print $image;
# done
[download]

BUT... in my experience, standard browsers do not display .bmp files. Perhaps you were using 'bmp' in a more generic sense to mean 'graphic'. If so, just substitute the appropriate MIME type in the Content-type line.