Я так и не понял,как в autoit  получать доступ к глобальной переменной из функции.

#include <GUIConstantsEx.au3>
#include <GDIPlus.au3>
#include <WinAPIGdi.au3>
#include <Array.au3>

Local $hGUI = GUICreate("Image show", 1000, 700)
Local $Array_Base[100] 

Local $idButton1 = GUICtrlCreateButton("1", 0, 600, 50,50)
Local $image_counter
$image_counter  = find_files()

_ArrayDisplay( $Array_Base)

Local $counter = 0

GUISetState(@SW_SHOW, $hGUI)

While 1
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE
ExitLoop
case $idButton1

$counter =  $counter + 1
GuiCtrlSetData($idButton1,$counter)
draw_image($Array_Base[$image_counter-$counter])

EndSwitch
WEnd

func draw_image($sFileName)
_GDIPlus_Startup()
Local $hImage = _GDIPlus_ImageLoadFromFile($sFileName)
Local $hGraphic = _GDIPlus_GraphicsCreateFromHWND($hGUI)
_GDIPlus_GraphicsDrawImage($hGraphic, $hImage, 0, 0)
_GDIPlus_Shutdown()
EndFunc

func find_files()
Local $hSearch = FileFindFirstFile("*.png*")
Local $image_counter = 0

Local $sFileName = ""
While 1

$sFileName = FileFindNextFile($hSearch)
 $image_counter =  $image_counter  + 1
_ArrayPush( $Array_Base, $sFileName,1)
If $sFileName ="" then ExitLoop

WEnd
FileClose($hSearch)
return $image_counter
EndFunc

Оказывается я просто был невнимателен и функцию вызывал до определения переменной!

#include <GUIConstantsEx.au3>
#include <GDIPlus.au3>
#include <WinAPIGdi.au3>
#include <Array.au3>

Local $hGUI = GUICreate("Зачем такое нужно 2?", 1000, 700)
Local $Array_Base[100] 

Local $idButton1 = GUICtrlCreateButton("1", 0, 600, 50,50)
Local $image_counter = 0
find_files()

_ArrayDisplay( $Array_Base)

Local $counter = 0

GUISetState(@SW_SHOW, $hGUI)

While 1
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE
ExitLoop
case $idButton1

$counter =  $counter + 1
GuiCtrlSetData($idButton1,$counter)
draw_image($Array_Base[$image_counter-$counter])

EndSwitch
WEnd

func draw_image($sFileName)
_GDIPlus_Startup()
Local $hImage = _GDIPlus_ImageLoadFromFile($sFileName)
Local $hGraphic = _GDIPlus_GraphicsCreateFromHWND($hGUI)
_GDIPlus_GraphicsDrawImage($hGraphic, $hImage, 0, 0)
_GDIPlus_Shutdown()
EndFunc

func find_files()
Local $hSearch = FileFindFirstFile("*.png*")

Local $sFileName = ""
While 1

$sFileName = FileFindNextFile($hSearch)
 $image_counter =  $image_counter  + 1
_ArrayPush( $Array_Base, $sFileName,1)
If $sFileName ="" then ExitLoop

WEnd
FileClose($hSearch)

EndFunc