A labeled DNA sequence may be reconstructed by hybridization with a given number of complementary oligonucleotides included in a library. Such a library acts as an optical sensor, in which integrated elements emit signals make fluorescent microimages. Specificity of changes in optical density caused by specific interactions between pairs of DNA bases depends on the known nearest neighbor model that has been assumed here as the background. In the paper, problems concerned with optical detection and interpretation of changes in optical response, which can be induced by changes in a given DNA sequence composition, are presented. Reliability of the fluorescence image analysis in investigating the DNA chains is discussed. To know the standard set of microimages specifying the correct sequence composition, comparative studies of abnormal composition can be made by analysis of changes in light intensity occurring in particular sites of the library.