In this paper, the time-integrated image pattern of spatial distribution and time-resolved image of optical radiation are measured in the normal direction from the rear side of targets by employing optical streak camera on the 100 TW femtosecond laser facility. The image pattern of spatial distribution presents a strip-shape: the region of optical radiation has a radiation angle and optical intensity distribution, and contains various components; the time-resolved image of optical radiation presents the time-resolved pattern of the optical radiation, witch further proves that the transition radiation is intense, which has short duration (ps) and correspouns to duration of TR of 85.5 ps. and other optical radiations are weak, which have very long duration (ns). The time-resolved characteristic of optical radiation can provide new evidence for discrimination and judgement of TR.