A new device is proposed where the electrode is a transparent electrode in modified SnO2. With this new electrode the reduction of oxygen occurs in a way similar to a gold electrode. Simultaneously the oxygen current is recorded versus time and picture of the interface itself is taken with a digital camera through the electrode. An image analysis is performed to determine the coated area and the number of objects by surface unit. Under cathodic protection, the reduction of oxygen induces an increase of the interfacial pH and then formation of scale deposit. The usual chronoamperometric analysis was completed by an in situ observation of the scale deposit. In natural water the biofilm. development was studied by electrochemical method to determine the biofilm thickness and this analysis is completed by a direct observation through the electrode. A good correlation between the two techniques was found.