a scanner which detects a side of {HEAD ~ a sheet} on which {TAIL ~ an image} is formed using a thermally decolorable coloring agent 
a scanner which detects a side of { HEAD ~ a sheet } on which { TAIL ~ an image } is formed using a thermally decolorable coloring agent
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH