Since Yarbus, it is well known that task greatly influences the visual exploration of a scene. In this paper, we quantify the influence of three different cognitive tasks on the visual exploration of various natural scene images. Eye movements made to solve the three tasks were compared to the ones recorded during a free-exploration condition. Eye movement parameters and eye fixation positions were compared during the time course of the exploration according to fixation/saccade rank. Tasks were chosen because they implied different visual processing and might be classified according to their difficulty. We found that task difficulty impacts eye-movement characteristics at the very beginning of exploration. The variability between eye fixations of observers is also impacted. Finally, eye-movement characteristics might reveal the tasks solving.