Due to all the discussion over this particular cel 
I found I couldn't resist trying to find it and 
confirm my suspicions.  I am 99% sure that this is 
a gorgeous fan cel done by someone with great 
talent.  It comes from the Future Trunks Special 
about 31.5 minutes into the show(sans commercial). 
 Not from any flashback in the series anywhere.  
And I checked both flashback sequences and the 
episode where Trunks returns to the future just in 
case it may have been there.  While it is very 
close, the discrepancy shows in his shirt 
specifically.  The shadowing that is present in 
every shot of the sequence is NOT in this cel.  
Plus the backgound is incorrect.  There are no 
flames present just the buildings.  Plus the 
mention of the fact that there are no sequence 
numbers on the cel itself are evident in this 
scan.  If anyone cares to challenge this I CAN and 
WILL provide the screen cap from the movie just to 
prove I am correct.