#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?s)<a\s[^>]*?href\s*=\s*\\'https?://site\.ru/[^>]+>\s*<img.+?</a>"
Local $sString = "<a class=\'fancybox\' href=\'http://site.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' rel=\'group\'><img src=\'http://site.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' width=\'400px\'></img></a>" & @CRLF & _
"<a class=\'fancybox\' href=\'http://site2.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' rel=\'group\'><img src=\'http://site2.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' width=\'400px\'></img></a>" & @CRLF & _
"<a class=\'fancybox\' href=\'http://site.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' rel=\'group\'><img src=\'http://site.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' width=\'400px\'></img></a>"
Local $sSubst = ""
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