Display Low-Res Versions Only
Never put your full resolution images on your website. It is not necessary for viewing, creates lag for your website, and gives art thieves more options for printing your stolen art at a high quality. Images for social media needn't be more than 1200px-1500px on the longest side at 72dpi. That's a good limit for your portfolio images as well.
Add A Copyright Disclaimer to Your Website
Giving potential art thieves a warning can be an effective deterrant. Your website should have a copyright disclaimer, which you can add visibly without being overbearing. The disclaimer I use in my website footer, which you are welcome to copy-paste is:
ALL IMAGES CONTAINED HEREIN © FIRSTNAME LASTNAME, UNLESS OTHERWISE SPECIFIED. NO IMAGE MAY BE USED IN PART OR ENTIRETY WITHOUT WRITTEN PERMISSION.
Expose Art Theft When it Happens
Public shaming is an affective deterrent for art theft. If you see a company selling pirated art, spreading the word online through your social circles can have a great influence on their reputation and pressure them to remove the pirated art. When it comes to AI images, it can be hard for some people to spot the signs and there is no obligation for a company or individual to mark images as AI generated. Encourage your art-appreciating friends to research the artist they are buying from to see their process images. That can help with identifying ethically-made art.
Support Ethical AI
There is a world where artists benefit from generative AI. As it currently stands, there are no generative AI tools that compensate creatives for their data, to my knowledge. It is important to define what AI developers can do to make their products ethical towards creatives, which is to train AI with data that has been obtained with explicit permission and fairly compensate the copyright owners (artists or to those who purchased the copyright) for it. This is no different than the concept behind art licensing, a common practice for companies paying an artist to use existing artwork for a new commercial purpose under a defined contract.