#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(<img.*?src=")((?:\w+\/)+?)([\w-]+\.(?:jpg|jpeg|png|gif))""
Local $sString = "<img src="index_files/bottle2.jpg" name="product ds Grodsdwth" class="pullleft">" & @CRLF & _
"" & @CRLF & _
"<img title="" src="index_files/ss-button.png" class="step-btn" alt=""></a>" & @CRLF & _
"" & @CRLF & _
"<img src="index_files/a/bottle2.jpg" name="product ds Grodsdwth" class="pullleft">"
Local $sSubst = "$1{#CDNPath#}img/$3""
Local $sResult = StringRegExpReplace($sString, $sRegex, $sSubst)
MsgBox($MB_SYSTEMMODAL, "Result", $sResult)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm