Alt text can be added to a DotNetNuke image either at the time of adding the image to the text content, or subsequently if required.
DotNetNuke manages uploaded images and documents through the File Manager.
I prefer to use the file manager to upload and manage my images and documents separately from when inserting content to the page.
With the background work done, images and documents uploaded, I can compose my content for the page, without the disruption involved in uploading an image.
While composing the page content I can click on the image icon within the editor to popup the Image Manager dialogue to make my selection.
Using the popup Image Manager navigate to and select the image which you wish to insert into your text.
Add further details regards the image, for example the size of the image, width or height, and the element which we are interested in the alt text.
Later on, if you decide to change the text right click on the image to select the properties option, this will open the Properties dialogue.
Why add ALT Text to an Image? Well adding alt text to an image is good for SEO, lets visitors understand the context in which you are using the image and for those who are using a screen reader to view your website the text will be spoken.