# A Crowdsourcing Recommendation Model for Image Annotations in Cultural Heritage Platforms
## 1 Introduction
Galleries, libraries, archives, and museums (GLAMs) are among the many organizations that have developed major efforts in the processes of digital transformation in recent years, but it is uncommon that they have the resources to properly characterize their digital collection assets, which results in metadata that are typically restricted by the vocabulary, taxonomies, and perspective managed by the specific institution [14]. The limited annotations and the semantic gap that exists between experts and the public will have a negative impact on the CH institution, affecting its visibility and long-term relevance as well as providing a poor user experience on their platforms [15]. The European Union, the American Library Association, and UNESCO [16] have been urged to take advantage of such advances in ICT and launch digitalization projects along with digital collections in order to encourage people to actively engage with CH content [17; 18]. However, their major shortcoming is a lack of well-defined and rich annotations for most of the large number of items they comprehend. This type of issue has a significant impact on the accessibility and discoverability of available digital content and limits the usability of these resources in new and interesting ways, hence limiting the user experience. Metadata quality improvement and enhancement are crucial factors in the CH domain, where the inventory of items that must be described or transcribed is generally too large to be addressed through normal procedures due to the significant time, effort, and resources required [19]. Since it is quite rare for GLAMs and other CH organizations to have the capacity to adequately identify, describe, or enhance digital collection items, they have turned to investigate the potential of crowdsourcing, as the digitization of their artworks is critical for their appropriate promotion on the Internet [20; 21]. All around the globe, exploring the potential of crowdsourcing in the CH domain is a growing trend, with CHinstitutions starting to share metadata descriptions that need to be enhanced, corrected, or annotated, and soliciting public assistance to help improve them [22; 23]. More and more, these organizations encourage people to enrich artworks and cultural assets contributing their knowledge and expertise to help improve their descriptions [24], providing annotations voluntarily to complete existing characterizations of paintings, statues, buildings, or even the more intangible aspects of heritage mentioned above, just from pictures or available descriptions of the items from the organization collections or archives [25]. Of course, this approach falls squarely into the open debate in the literature about the advantages and disadvantages of collaborative efforts of interested users (social tags) compared to taxonomies developed by field experts (controlled vocabularies). Even though a large number of research works have been published in recent years [26; 27; 28; 29], it is possible to identify complementary strengths in each technique, and there are no conclusive conclusions about the superiority of a particular approach, the most adequate option being largely dependent on the application scenery, the available resources, and the evaluation criteria. In any case, the research presented in this paper is not affected by this open debate. We are not faced with the dilemma between social tags and controlled vocabularies when implementing a given system. This work is focused on scenery where human resources are certainly scarce, and it is aimed at developing technological tools to improve the effectiveness of the open collaborative effort approaches. While crowdsourcing systems face the challenge of reaching and utilizing an adequate number of available individuals, it is ultimately up to individual persons to discover assets that best match their interests or preferences, even though there is no monetary compensation for participation (the final result should be sufficiently rewarding for these kinds of volunteers).