This seems to work for tif and jpeg files [change the extension in 2 places to switch between file types for this demo]
William
#Include <Array.au3>
#include <File.au3>
#Include <String.au3>
Global $sInImage= FileOpenDialog ("Test File","C:\Documents and Settings\Owner\Desktop\SBACC Comp nov2013\possibles","All(*.*)")
Global $Testfile = StringReplace ($sInImage,".tif",".txt")
RunWait (@ScriptDir&'\i_view32.exe "'& $sInImage & '" /info="'&$Testfile&'"','')
$file= FileOpen($Testfile)
$text = FileRead($file)
FileClose($file)
$adimensions = _StringBetween($text,"Image dimensions =","Pixels")
$aHtWid = StringSplit ($adimensions[0]," x ",1)
$wid = StringStripWS($aHtWid[1],8)
$ht = StringStripWS($aHtWid[2],8)
MsgBox (0,"Wid x Ht", $wid&"x"&$ht)
FileDelete ($Testfile)
exit