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Unless I've misunderstood, I'm not sure that aria-hidden is going to be able to deliver what you are looking to do - I don't think you can use it to hide the alt attribute of the image without hiding the image as well. If you mean adding non-alt-attribute text to the page so that it is visible to sighted users, I would expect that it would make sense to keep that accessible to screen readers as well - it should be useful to all kinds of site visitor, I would have thought. In general, I would tend to suggest that alt attributes should primarily be used for their intended accessibility purpose, and that this should tend to include more valuable content on the page which the search engines may find useful. I found this guide to be one of the best I have seen on the subject. As a sidenote, I tend to think alt attributes are over-rated for SEO purposes anyway. In our testing, we have not yet detected a statistically significant uplift from adding alt attributes to images that did not previously have them. Good luck!