This paper presents an overview of the ImageCLEF 2023 lab, which was organized in the frame of the Conference and Labs of the Evaluation Forum – CLEF Labs 2023. ImageCLEF is an ongoing evaluation event that started in 2003 and that encourage the evaluation of the technologies for annotation, indexing and retrieval of multimodal data with the goal of providing information access to large collections of data in various usage scenarios and domains. In 2023, the 21st edition of ImageCLEF runs three main tasks: (i) a medical task which included the sequel of the caption analysis task and three new tasks, namely, GANs for medical images, Visual Question Answering for colonoscopy images, and medical dialogue summarization; (ii) a sequel of the fusion task addressing the design of late fusion schemes for boosting the performance, with two real-world applications: image search diversification (retrieval) and prediction of visual interestingness (regression); and (iii) a sequel of the social media aware task on potential real-life effects awareness of online image sharing. The benchmark campaign was a real success and received the participation of over 45 groups submitting more than 240 runs.