Код:

@Echo Off &Cls
Set "BoxIn=Z:\Box_In"
Set Mask="*.jpg"
Set "BoxOut=Z:\Box_Out"
Set /A n=3
Pushd "%BoxIn%"||(Echo Folder "%BoxIn%\" not found &Pause &Exit /B 2)
Set /A m=10000, i=0
For /F "usebackq delims=" %%f In (`2^>nul Dir /B /A:-D /O:D %Mask%`) Do (
Call :MyMove "%%f"
)
Pause
Exit /B
:MyMove
Set /A remain=%i%%%%n%
If Not %remain% EQU 0 (>nul Move %1 "%Out%\" &Set /A i+=1 &Exit /B)
Set /A m+=1
Set "Out=%BoxOut%\%m:~1%"
Md "%Out%" &Set /A i+=1
>nul Move %1 "%Out%\"
Exit /B