When selecting an item, all the relevant information is shown in a user-friendly way. Unknown information can be easily added by answering the questions, which will be saved into OpenStreetMap directly (this requires a free account).
An (anonymous) review can be left for some types of features, hosted by https://Mangrove.reviews, a libre and open data review project.
Images are fetched from various sources, such as Panoramax, Wikipedia and Mapillary. New images can be contributed to Panoramax directly from within MapComplete.