In your knowledge base article, website page, landing page or blog, hover over the image and click the pencil icon. Scroll to where it says Alt text and type in the copy, then click Apply changes.
From your Hubspot dashboard, go to either your Knowledge Base, Website Pages, Landing Pages or Blog.
Click on an existing page or create a new one.
Hover over the image and click on the pencil icon.
Scroll down to where it says Alt Text and add in the copy you would like to use.
Scroll to the bottom and click Apply changes.