Many third party apps, and even stock apps on some devices have graphical content that has no labels or help tags to advise the user what that content stands for. Maybe you have heard it said, a picture is worth a thousand words, but I'm here to tell you, without a couple of words in the right place for each picture, the point is completely lost on a poor blind man like me.
When exploring the screen with talkback, you may hear messages saying graphic, followd by a two or three digit number. This means you have encountered a picture that has no text label or help tag. It may be a place holder. It may be a graphical button which you need to touch to activate a feature of the app. You as a blind person wouldn't know unless you activated that thing to find out what it does. At that, activating the item might not tell you anything. If the item is only a placeholder, then nothing will happen. suppose the object is the shuffle button in a music app, only you don't have music playing at the moment and even if you did, you would have to wait for the start of the next song before you realized something had changed. Something may change visually on the screen but you wouldn't see the result and may not notice any change until the next time you explore that area of the screen.
Developers need to be highly aware of this issue because it can be resolved from the ground up by simply adding labels whenever a new button or control is added to the layout. What it does for the talkback experience can not be overstated. It will also help users when full voice control becomes a reality on android. It looks nice for sighted users and there is no compelling reason not to label other than habit.
Talkback users can add their own custom labels to graphics starting in Jellybean 4.3. Obviously this is great for users who are running the latest and greatest, but it will take a long time before most users have access to this feature. There are also the drawbacks stated above. For best effect, a user really should get a sighted person to help identify the graphics initially which creates a dependency. Finally, it isn't possible yet to back up the graphics label files. users can not share predefined sets of labels between devices or amongst the community.
If you need to use talkback to label graphics, and all the stars are aligned so that you can access this feature, here is how you go about it.
Touch a graphic on the screen and hear talkback announce the word graphic followed by a number.
Draw two lines on the screen, one from the bottom up, then another from the top of your first line to the right. The Up right gesture opens a context menu.
Explore the screen in a circle with one finger until you find the add label button. Then lift your finger.
Enter the text you want to associate with your graphic and touch the done button in the lower right corner of the keypad.
Now when you touch your graphic, talkback will announce the text you typed previously.
Once you have labeled a graphic, performing the up right gesture on that graphic reveals two new options, edit and remove.