If you insist of not having bmp files, here a better script :
#include <GDIPlus.au3>
#include <GUIConstants.au3>
#include <WinAPIGdi.au3>
#include <String.au3>
Login()
Func Login()
_GDIPlus_Startup()
Local $hImageHide = _GDIPlus_BitmapCreateHBITMAPFromBitmap(_ConvertStringToImage1(21, 17))
Local $hImageShow = _GDIPlus_BitmapCreateHBITMAPFromBitmap(_ConvertStringToImage2(21, 17))
GUICreate("Login", 200, 100)
GUICtrlCreateLabel("", 10, 10, 180, 19)
GUICtrlSetState(-1, $GUI_DISABLE)
GUICtrlSetBkColor(-1, 0x86BEEF)
GUICtrlCreateLabel("", 11, 11, 178, 17)
GUICtrlSetState(-1, $GUI_DISABLE)
GUICtrlSetBkColor(-1, 0xFFFFFF)
Local $idInput = GUICtrlCreateInput("", 14, 11, 154, 17, $ES_PASSWORD, $WS_EX_TOOLWINDOW)
Local $idEye = GUICtrlCreatePic("", 168, 11, 21, 17), $bHide = True
Local $iDefault = GUICtrlSendMsg($idInput, $EM_GETPASSWORDCHAR, 0, 0)
GUICtrlSendMsg($idEye, $STM_SETIMAGE, $IMAGE_BITMAP, $hImageHide)
GUISetState()
While True
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE
ExitLoop
Case $idEye
$bHide = Not $bHide
GUICtrlSendMsg($idEye, $STM_SETIMAGE, $IMAGE_BITMAP, $bHide ? $hImageHide : $hImageShow)
GUICtrlSendMsg($idInput, $EM_SETPASSWORDCHAR, $bHide ? $iDefault : 0, 0)
_WinAPI_RedrawWindow(GUICtrlGetHandle($idInput))
EndSwitch
WEnd
_GDIPlus_Shutdown()
EndFunc ;==>Login
Func _ConvertStringToImage1($iWidth, $iHeight)
Local Const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
Return _ReadImageFromText($IMAGE, $iWidth, $iHeight)
EndFunc ;==>_ConvertStringToImage1
Func _ConvertStringToImage2($iWidth, $iHeight)
Local Const $IMAGE = "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"
Return _ReadImageFromText($IMAGE, $iWidth, $iHeight)
EndFunc ;==>_ConvertStringToImage2
Func _ReadImageFromText($sString, $iWidth, $iHeight, $bFileName = False)
; Recreate image from text
If $bFileName Then $sString = FileRead($sString)
Local $dData = Binary("0x" & $sString)
Local $tByte = DllStructCreate("byte string[" & $iWidth * $iHeight * 4 & "]")
DllStructSetData($tByte, "string", $dData)
Return _GDIPlus_BitmapCreateFromScan0($iWidth, $iHeight, $GDIP_PXF32ARGB, $iWidth * 4, DllStructGetPtr($tByte))
EndFunc ;==>_ReadImageFromText