Securing those environment variables is not needed, since you don't spawn any kids.

You're using the wrong MIME type for "JPEG" images. It's should be image/jpeg.

die is not very appropriate for CGI scripts.

exit is not needed.

sysread is probably more appropriate, but I find $/ = \2048 and $/ = \$buffer_size neat:

local $/ = \2048;
open(my $fh, '<', $path) or die "Failed to open $path: $!";
binmode($fh);
binmode(STDOUT);
print while <$fh>;
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