In order to simulate the mechanical behavior of laminated carbon fiber reinforced polymers (CFRP) for automotive as well as for aerospace applications, numerical models based on cohesive zones are usually used. The codes of these models request for different interlaminar properties - including energy, stress and displacement related parameters - under Mode I, Mode II and mixed Mode loading conditions. The current work focuses on the determination of the interlaminar fracture toughness, under Mode I loading conditions of a double cantilever beam (DCB) specimen. Multiple methodologies from different international standards and further common techniques are compared and discussed. The novelty lies within the improvement of the testing setup concerning the metrology by using digital image correlation (DIC) as an extensometer as well as for crack growth measurements. Besides a sensitivity analysis, including crack length measurement, the work also includes a more detailed insight into the constraints of different methods presented in the different standards. An outlook will be given by deduction of a material model based on detailed DIC investigations.