Experimental evidence suggests DNA mechanical properties, in particular intrinsic curvature and flexibility, have a role in many relevant biological processes. Systematic investigations about the origin of DNA curvature and flexibility have been carried out; however, most of the applied experimental techniques need simplifying models to interpret the data, which can affect the results. Progress in the direct visualization of macromolecules allows the analysis of morphological properties and structural changes of DNAs directly from the digitised micrographs of single molecules. In addition, the statistical analysis of a large number of molecules gives information both on the local intrinsic curvature and the flexibility of DNA tracts at nanometric scale in relatively long sequences. However, it is necessary to extend the classical worm-like chain model (WLC) for describing conformations of intrinsically straight homogeneous polymers to DNA. This review describes the various methodologies proposed by different authors.