Apparatus and methods for use with a blood sample are described. The blood sample is stained with a first dye that predominantly stains DNA, and a second dye that stains at least one other cellular component being different from DNA. A plurality of images of the blood sample are acquired. A candidate object is identified as being a candidate of a given entity. A first stained area, which is stained by the first dye and which is disposed within the candidate object, is identified. A second stained area, which is stained by the second dye and which is disposed within the candidate object, is identified. The entity is detected by determining that features of the stained areas satisfy predetermined criteria associated with the entity. Other applications are also described.