Single-frequency piezoresponse force microscopy (PFM) images of a BiFeO3/DyScO3(110) thin film, obtained with long (k(c)=0.82N/m) and short (k(c)=7.64N/m) cantilevers, were analyzed as a function of the applied voltage frequency. For long cantilevers, the electrostatic and electrostrictive contributions were identified. These contributions were reduced with a frequency near the second mode of the contact resonance; while for short cantilevers, the first mode was necessary. A method for domain structure analyses, to discriminate a ferroelectric behavior from a non-ferroelectric, through the optimization of PFM images, is also described. The analysis can be extended to cantilevers with different spring constants and ferroelectric materials.