Speckle photography interferometry (SPI) is used to evaluate the stress-strain behaviour of animal bones under loads by recording the speckle fields generated on the bone surface and thus finding the relationship between the fractal dimension D(s) and the compression load P. The procedure consists of application of slow and monotonous compression loads, and recording of the deformation levels and vertical displacements of the specimen. A He-Ne laser beam directed at the surface of bone specimen produces light scattering which generates the speckle. The optical fields show significant differences before and after fracture, due to the changes of the bone surface generated by the strain. Our results support previous suggestions of a relationship between fractal characteristics and parameters related to the mechanical behaviour of materials.