The notion of biometric categorisation as used in this Regulation should be defined as assigning natural persons to specific categories on the basis of their biometric data. Such specific categories can relate to aspects such as sex, age, hair colour, eye colour, tattoos, behavioural or personality traits, language, religion, membership of a national minority, sexual or political orientation. This does not include biometric categorization systems that are a purely ancillary feature intrinsically linked to another commercial service meaning that the feature cannot, for objective technical reasons, be used without the principal service and the integration of that feature or functionality is not a means to circumvent the applicability of the rules of this Regulation. For example, filters categorizing facial or body features used on online marketplaces could constitute such an ancillary feature as they can only be used in relation to the principal service which consists in selling a product by allowing the consumer to preview the display of the product on him or herself and help the consumer to make a purchase decision. Filters used on online social network services which categorise facial or body features to allow users to add or modify pictures or videos could also be considered as ancillary feature as such filter cannot be used without the principal service of the social network services consisting in the sharing of content online.