Over the last few years, social network systems have greatly increased users' involvement in online content creation and annotation. Since such systems usually need to deal with a large amount of multimedia data, it becomes desirable to realize an interactive service that minimizes tedious and time-consuming manual annotation. In this paper, we propose an interactive online platform that is capable of performing semi-automatic image annotation and tag recommendation for an extensive online database. First, when the user marks a specific object in an image, the system performs an object duplicate detection and returns the search results with images containing similar objects. Then, the annotation of the object can be performed in two ways: (1) In the tag recommendation process, the system recommends tags associated with the object in images of the search results, among which, the user can accept some tags for the object in the given image. (2) In the tag propagation process, when the user enters his/her tag for the object, it is propagated to images in the search results. Different techniques to speed-up the process of indexing and retrieval are presented in this paper and their effectiveness demonstrated through a set of experiments considering various classes of objects.