Active thermography is an infrared-based technique for nondestructive testing of materials. It often uses advanced evaluation techniques based on temperature spatial and temporal changes. Results of active thermography are contrast differences, which indicate possible defects in an inspected material. These differences cannot be quantified by temperature. This contribution is focused on the active thermography results' evaluation parameters and the contrast-to-noise ratio method, which can be used for quantitative evaluation of the results. Different result interpretation procedures are introduced. The influence of a selection method for indication and reference regions and the effect of image scaling on inspection results are discussed.