Photo annotation: a survey

Due to the large number of photos that are currently being generated, it is very important to have techniques to organize, search for, and retrieve such images. Photo annotation plays a key role in these mechanisms because it can link raw data (photos) to specific information that is essential for human beings to handle large amounts of content. However, the generation of photo annotation is still a difficult problem to solve as part of a well-known challenge called the semantic gap. In this paper, a literature review was conducted with the aim of investigating the most popular methods employed to produce photo annotations. Based on the papers surveyed, we identified that People (“Who?”), Location (“Where?”), and Event (“Where? When?”) are the most important features of photo annotation. We also established comparisons between similar photo annotation methods, highlighting key aspects of the most commonly used approaches. Moreover, we provide an overview of a general photo annotation process and present the main aspects of photo annotation representation comprising formats, context of usage, advantages and disadvantages. Finally, we discuss ways to improve photo annotation methods and present some future research guidelines.