Quality of metal-matrix composite castings, similarly as quality of conventional metal castings is defined by the collection of data concerning chemical constitution, properties (e.g. strength) and structure of final products. During study aimed at determining these parameters, the priority is to maintain the highest possible repeatability and automation of measurement. In case of chemical constitution or mechanical properties analysis it is considerably easy to achieve thanks to application of appropriate research procedure. Analysis of structure of studied materials is however a much bigger problem. To improve it, different tools of digital image analysis are being used, but because of only slight differences (e.g. in color) between different elements of structure, conducting such analysis without performing additional study may result in obtaining false results. In such case, identification of an object is very important: unequivocal conclusion whether a given object is a reinforcement or maybe an impurity or an inclusion foreign matter, or is it a structure of improper, unintentional chemical constitution. It is particularly important concerning composites for which on the images obtained using both optical and scanning microscopy individual phases (reinforcement, matrix and impurities) are difficult to distinguish. In such case identification of particular phases is aimed at avoiding mistakes, for example while analyzing the quantity or uniformity of spacing of reinforcement phase in given space. X-ray diffraction may be a solution for this problem. An example of identification (quantitative and qualitative description) of reinforcement phase in suspension composites is presented further in the paper. The authors present also a chemical constitution of selected elements of structure of metal-matrix composites from ex-situ group.