A group of research projects based at HP-Labs Bristol, the University of Bristol and ARKive (a new large multimedia database project focused on the worlds biodiversity based in the UK) are working to develop a flexible model for the indexing of multimedia collections that allows users to 'annotate' content utilising extensible controlled vocabularies. As part of the educationally focused ARKive-ERA project a series of models for user annotation have been developed. The need for these types of user support and tools was identified while conducting pre-design stage user studies with specialist user groups. The needs centre around the limitations of current on-line museum and library systems that do not provide support for users to annotate or 'tag' multimedia objects of relevance to their particular community of interest or with specialised indexing terms. This would enable specialised resource discovery and knowledge sharing with other members of their communities. One example is that of University Lecturers and Researchers studying a particular type of animal behaviour. They may wish to identify all relevant images or video of that particular behaviour and annotate them as good illustrations of aspects of that behaviour. However significant issues arise over for example, the validation of information, access control and the use of such annotations by the resource discovery tools. The paper explores these and other issues and problems involved and how the various models can help provide solutions to the key problems and thus meet the needs of a diverse range of 'communities of interest' and adding significant value to on-line multimedia collections.