Avoid ableist assumptions when and if you can. No presenter and no artifact is perfect, but to try to make a poster accessible is a step in the right direction.
From the start use a template that allows your poster to be easily translated to a PDF reader. (PowerPoint or other). Because so many posters are first created in PowerPoint due to its great editing--> printing capabilities for posters, use these guidelines for creating posters.
https://webaim.org/techniques/powerpoint/.
Include a QR code on your poster so that others may download the poster and have it read to them with a screen reader or other adaptive device. You can provide an accessible PDF or plain text version of your poster's content.
In those templates, give each photo, chart, plot, or graph appropriate alt text or label them as decorative text.
NOTE: Alt text for any image should have the equivalent of a full caption within it (label, title, caption sentences that explain what is in the chart/image/data field shown using full sentences), and a citation if needed.
Confirm that a screenreader can decode your poster (created in PowerPoint) in the right order, which will then cascade into any PDF or other file that you create with the slide/poster template. This can be done by manipulating elements via the "Arrange" tab. More information on that can be found via these help sites:
Special considerations must be taken to make math and equations accessible. These resources are a good start.
Think about color blindness issues. Use online tools to check your images, graphs, and charts.
Avoid tables.
Avoid background images; opt for plain white backgrounds for posters.
Use this detailed guide for more thoughtful approaches.
[ https://www.aucd.org/docs/annual_mtg_2008/accessibility_posters_gilson2007.pdf ]
EU Standards for Accessibility
USA Standards for Accessibility (US Access Board)
United Nations Convention on the Rights of Persons with Disabilities