This paper presents new methods for extracting semantic knowledge from collections of annotated images. The proposed methods include novel automatic techniques for extracting semantic concepts by disambiguating the senses of words in annotations using the lexical database WordNet, using both the images and their annotations, and for discovering semantic relations among the detected concepts based on WordNet. Another contribution of this paper is the evaluation of several techniques for visual feature descriptor extraction and data clustering in the extraction of semantic concepts. Experiments show the potential of integrating the analysis of both images and annotations for improving the performance of the word-sense disambiguation process. In particular, the accuracy improves 4-15% with respect to the baselines systems for nature images.