Disclosed is a method of assessing a structural defect presence in a structure, the method comprising the steps of: determining at least one critical damage strain value of the structure, capturing a first image of a surface of the structure under a first loading condition; capturing a second image of the surface of the structure under a second loading condition; assigning a position matrix on the captured first image; obtaining a deformation matrix comprising a deformation value at each position of the position matrix by using an image correlation technique on the first and second images, and by comparing deformation of corresponding parts of the surface captured therein; calculating a strain matrix using the obtained deformation matrix; and determining a micro-crack to be present at a position if an element of the strain matrix representing the strain at the position is greater than or equal to a predetermined critical damage strain value, wherein the critical damage strain value is a strain value at which a micro-crack is detected or predicted to appear and/or propagate.