Even though vision-based methods for displacement measurement have been used in civil engineering for more than a decade,most of those techniques required some sort target attachment.The targets,simple figures such as known-dimension circles or rectangles,play important roles for analysis of data mainly for the following: 1) dominant markers of measuring location,and 2) calibration rules for converting displacement in pixel unit to length unit.Using target attachment techniques for real-life structures such as bridges is not practical in most of the cases.This is due to the fact that the monitored locations always are generally located trnder the bridge deck,or due to access limitations etc.