@echo off
title File Rotation Service Login.
echo Hello, please log in with your user ID.
echo Username:
set /Z user
if %user%==(Bussjaeger) goto password
cls
echo Username not found in database!
:password
set/p "pass=Password"
if %pass%==(12345) goto correct
cls
echo Incorrect Password!
ping localhost -n 3 >nul
attrib +s +h (This file's name)
:correct
echo Welcome Mr.Bussjaeger. Activating file rotation..
TIMEOUT /T 3
:Start
Set "SrcDir=E:Schem"
Set "ExtLst=*.jpg *.png *.gif"
Set "i=0"
For /F "Delims=" %%A In ('Where /R "%SrcDir%" %ExtLst%') Do (Set /A i+=1
    Call Set "$[%%i%%]=%%A")
Set /A #=(%Random%%%i)+1
Call Start "" "%%$[%#%]%%"
TIMEOUT /T 10000
goto Taskkill
:Taskkill
taskkill /IM Microsoft.Photos.exe /F
goto Start

@echo off
title File Rotation Service Login.
rem Variables are set to blank to avoid them to have old strings set in the memory.
set user=
set pass=

:start
cls
echo Hello, please log in with your user ID.
set /p user=User (Case sensitive):
rem The IF command will be case sensitive if the /i option is not used.
rem In order to avoid case sensitive, the command should be:
rem if /i "%user%" == "Bussjaeger" (
if "%user%" == "Bussjaeger" (
goto password
) else (
cls
echo Username not found in database!
echo Press any key to try again . . .
pause > nul
goto start
)

:password
set /p pass=Password:
if "%pass%" == "12345" (
goto correct
) else (
cls
echo Incorrect Password!
goto password
)

rem What is the use of the next two lines?
ping localhost -n 3 >nul
attrib +s +h (This file's name)

:correct
echo Welcome Mr.Bussjaeger. Activating file rotation..
timeout /t 3

:start_work
set "srcdir=e:schem"
set "extlst=*.jpg *.png *.gif"
set "i=0"

rem The following line will fail. Sixtax is not correct.
for /f "delims=" %%a in ('where /r "%srcdir%" %extlst%') do (
    set /a "i+=1"
    call set "$[%%i%%]=%%a"
)
set /a #=(%random%%%i)+1

rem Not sure what the following lines should do.
call start "" "%%$[%#%]%%"
timeout /t 10000
goto taskkill

:taskkill
taskkill /im microsoft.photos.exe /f
goto start