Just tried this code in May 2020 works for .gif .png but was returning blank results for .jpg files. The file type was recognised but the size marker string was not found. 
$  file sample.jpg
sample.jpg: JPEG image data, JFIF standard 1.01, resolution (DPI), den
+sity 123x123, segment length 16, progressive, precision 8, 1024x1448,
+ frames 3
$ perl -v
This is perl 5, version 22, subversion 1 (v5.22.1) built for darwin-th
+read-multi-2level

$ hexdump -C sample.jpg | head -30
00000000  ff d8 ff e0 00 10 4a 46  49 46 00 01 01 01 00 7b  |......JFI
+F.....{|
00000010  00 7b 00 00 ff db 00 43  00 01 01 01 01 01 01 01  |.{.....C.
+.......|
00000020  01 01 01 01 01 01 01 01  01 01 01 01 01 01 01 01  |.........
+.......|*
00000090  01 01 01 01 01 01 01 01  01 01 01 01 01 01 >>>> ff c2 <<<<  
+ |................|
000000a0  00 11 08 >>> 05 a8 04 00 <<<< 03  01 22 00 02 11 01 03 11  |
+........."......|
000000b0  01 ff c4 00 1e 00 01 00  01 04 03 01 01 00 00 00  |.........
+.......|
000000c0  00 00 00 00 00 00 00 06  05 07 08 09 03 04 0a 02  |.........
+.......|

[download]
Looking for size bytes 05 a8 04 00 and a marker a few bytes before shows the marker to be ff c2 . Changing 
elsif ( $_[0] =~ m/^^\xFF\xD8.{4}JFIF/s  ) {
   $sig = 'JPEG';        # found JPG signature
 ($height,$width) = unpack( "nn", $1 )
    if $_[0] =~ /\xFF\xC0...(....)/s;

to

 elsif ( $_[0] =~ m/^^\xFF\xD8.{4}JFIF/s  ) {
  $sig = 'JPEG';
    ($height,$width) = unpack( "nn", $1 ) 
      if $_[0] =~ /\xFF\xC2...(....)/s;

along with the driver
 
  for my $img ( qw(  ./sample.jpg ./sampleC.jpg  ) ) {
        my $data = get_file($img);
        my @res = image_size($data);
        print "\nNative $img $res[2] width $res[0] height $res[1]\n";
        ($x, $y) = imgsize($img);
        print "Image::Size ($x, $y)\n"

[download]
gives a working code set. Adding the Image::Size method to test along size gives 
Native ./sample.jpg JPEG width 1024 height 1448
Image::Size (1024, 1448)

Native ./sampleC.jpg JPEG width 617 height 1220
Image::Size (617, 1220)

[download]
Not sure what changed or if this is just a mac thing but wanted to leave this testament for following monks.

In reply to Re: Image size in pure perl by gannett
in thread Image size in pure perl by Anonymous Monk

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