While AtoM does likely provide the functionality you need to display and describe digital images and data related to an artist, you're right in questioning whether it's the best tool for your particular use case.
AtoM is a tool that was created by and for archivists, meaning that it implements established national and international archival description standards, uses terminology from the archival profession throughout, and expects a certain base familiarity with archival concepts around arrangement and description from its users. If that's not you and/or your target users, then you might find yourself fighting against some of the aspects of the application to implement the setup you'd like to see.
If the system you want to set up is going to be more of a portfolio, then a content management site with appropriate themes/templates may serve you better - for example, Wordpress, etc. There are also a number of portfolio creation solutions out there, though I'm not familiar with open source options in this space, so you'll have to do some searching. If you're looking to manage, categorize, annotate, and share digital content, a Digital Asset Management System (DAMS) may be a better solution. There are a number of options both proprietary and open source in this space.
In any case, if you'd like to learn more about AtoM, here is a previous forum thread where I've shared some general project resources and links that may help you further evaluate whether or not AtoM will help meet your needs. See: