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