Alternative text (alt text) allows screen readers to capture the description and read it loudly, which provides help to people with visual disturbances. To add alt text to an item in PowerPoint.
Add Alt Text to Items in PowerPoint
As advanced as screen readers, they are still not sophisticated enough to understand what an object is or what an image represents How to make the computer read documents to you  To add alt text in PowerPoint, open your presentation and select the item you want to add alt text to.
On the "Format" tab, select "Alt text" in the "Availability" group.
Alternatively, you can right-click on the item itself and choose "Change alt text" from the drop-down menu.
Whatever method you choose, you will see the "Alt text" box displayed on the right side of the window on the page. There are a few things you can do here. You can manually type the alt text in the content box (1), have the PowerPoint generate a description for you (2) or select the object as decorative (3).
If you mark something as decorative, it is what it should be an object that is aesthetically pleasing but does not add any value to the actual content. Office uses a stylistic border as something you might want to mark as decorative, which is a good example.
Mark something as decorative by marking the box next to "Mark as decorative". When you do this, you will notice the box where you manually enter the alt text is grayed out and shows a message that screen readers will not retrieve the description.
You also have the options of allowing PowerPoint to generate a description of the selected object for you.
As you can see, PowerPoint gave "A close-up of a logo" as the alto to do so. our object and let the user know that the description was generated automatically. While office description is not wrong, it is not very useful.
If you would rather enter the alt text, select the text box and type the description. The general rule for alt text is to keep it concise and descriptive. You also do not need to add the words "picture of" or "photo of" before your description, because screen readers already announce an object as an image.
It is all there is to add alt text to your images. If you want to prevent PowerPoint from automatically generating alt text for your new images, you can disable this feature. To do so, select the "File" tab and then select "Options" at the bottom of the left pane.
The "PowerPoint Options" window appears. In the left pane, select "Ease of Access."
Next, find the section "Automatic Alt Text" and uncheck the box next to "Automatically create alt text for me," which is enabled by default. When you are selected, select "OK".
PowerPoint will now not automatically generate alttext for new images.