GetImageSize() seems confused on certain JPGs from freeservers.  The JPG is valid (you can load it from your web-browser).

Script to reproduce:
<?

$res = GetImageSize("http://guildprime.8m.net/bug.jpg");
if($res == FALSE)
{
  print("Erk! GetImageSize returned FALSE!");
} else {
  print_r($res);
}

print("<br><br>");

$res = GetImageSize("http://guildprime.8m.net/notbug.jpg");
if($res == FALSE)
{
  print("Erk! GetImageSize returned FALSE!");
} else {
  print_r($res);
}

?>

The script SHOULD report:
Array ( [0] => 396 [1] => 178 [2] => 2 [3] => width="396" height="178" [bits] => 8 [channels] => 3 ) 
Array ( [0] => 800 [1] => 600 [2] => 2 [3] => width="800" height="600" [bits] => 8 [channels] => 3 ) 

And it does when I copy the file to my local Apache web server and change the script to point there instead.  It also works on a second server I have running PHP 4.1.2.

However, with the URL listed, under PHP 4.3.0, it reports:
Erk! GetImageSize returned FALSE!
Array ( [0] => 800 [1] => 600 [2] => 2 [3] => width="800" height="600" [bits] => 8 [channels] => 3 [mime] => image/jpeg ) 

Configuration options:
./configure  --with-apxs --with-zlib --with-bz2 --with-gd=/usr --enable-gd-native-ttf --with-mysql=/usr --enable-sockets --prefix=/usr --with-ttf --enable-ftp

Troubleshooting steps already taken:
- I tried copying the image to my local web server, changed the script to look there, and it works.
- Dozens of other JPGs on freeservers work as well.
- It seems this combination of server and image file is causing GetImageSize() to fail.  When I point my web browser at the same URL, the picture comes up. 
- I tried putting the picture into GIMP and resaving out - the re-saved image also has the same problems.  (This file is bug2.jpg at the same site.)
- Running 'identify -verbose' on the files shows perhaps the difference of Resolution (notbug.jpg is 300x300 pixels/inch, as are most of the other pictures, while bug.jpg and bug2.jpg are at72x72 pixels/inch) may be part of what's triggering it.
- I have re-downloaded the source, re-compiled and re-installed with the above options, with no change in results.
- Running the script from the command line has no change in results.

All-in-all, quite strange...