@echo off
echo.
setlocal
set N=0
set FILENAME=baseFileName.%N%.tif
:loop
set /a N+=1
set FILENAME=baseFileName.%N%.tif
if exist %FILENAME% goto :loop
echo You can safely use this name %FILENAME% to create a new file
endlocal
But maybe it has elements of truth in it that may be useful for someone else?
Jumping out of an airplane is not a basic instinct. Neither is breathing underwater. But put the two together and you're traveling through space!