Hello @samben28
Thanks for checking out my plugin.
In the free-version, the alt text will always be the image filename. This is updated in the media library.
If you have Image Attributes Pro, you can use %posttitle% as the alt text and the alt text will be the title of the post to which the image is attached to.
Hope that clarifies your question, feel free to let me know if you have follow up questions. Thank you.