1. A system for use in monitoring one or more conditions of a subject's body, the system comprising a control unit configured as a computer system comprising: an input port configured to receive input data indicative of one or more measurement sessions applied to at least a portion of the subject's body, said input data comprising measured image data in the form of a sequence of speckle patterns generated by the portion of the subject's body during a certain time period of said one or more measurement sessions, and data indicative of parameter of at least one external stimulation applied to said portion of the subject's body during certain said time period; a non-transitory computer readable memory for storing one or more predetermined models, the model comprising data indicative of a relation between one or more measurable parameters and one or more conditions of the subject's body; and a processor configured to carry out the following: translating said sequence of the speckle patterns into a time varying spatial correlation function indicative of a change of the speckle pattern over time, said translating comprising determining a spatial correlation function between successive speckle patterns in the sequence, and determining the time varying spatial correlation function in the form of a time-varying function of at least spatial position of a peak of the correlation function indicative of the change of the speckle pattern over time; selecting at least one spatial feature of the time varying special correlation function corresponding to the parameter of the at least one external stimulus, and using said at least one selected spatial feature as the measurable parameter of the model, to determine one or more corresponding body conditions; and generating output data indicative of said one or more corresponding body conditions, and an output port configured to transmit the output data from to at least one device configured to present the output data to a user, the output data comprising at least one of the following: a graph of the temporal changes in the spatial correlation function; a value of one or more of extracted parameters, and a value of at least one body condition being determined.