Let's Be Real
Now anyone read the image caption (Small text below the image) can understand the image by looking at the image caption. Isn't it? Do you think it matters at all? I know... You don't wanna add image captions everytime for every image. But think about when presenting an image in your post or article. The image you add may worth more than 1000 words but basically if someone can't identify what's it about in first place, you are confusing some of your readers. However it depends. Some users might have hard time identifying the image you have added unless they have no idea what it is or if you haven't give them any clue about it. Remember, user experience matters :) It's just not about writing your heart out.
You might ask "WHY?" again. The image caption is just to elaborate the image. Unlike the alternative text, it has no SEO value in it. It provides the value for your readers and make your post or article much more user friendly. Anyway it depends on you. Depends on whether you write for search engines or real human beings. I'd say write for readers and if you do, consider adding image captions where necessary.
Image caption is not only about just describing what's there, but also you can add additional information if you need to, if that matters while reading your post or article. Just take a look at the image on this page ~ Apollo 13 at Mission Control, and read the description there. Even such a long description is possible as the image caption if it's relevant there.
I Just Did It
As you just witnessed an image caption on Blogger, you might wanna know how is it possible too. It's quite simple and easily accessible via image options. I'm gonna refer steps to follow in Blogger blogs, but even if you have a non-Blogger blog or writing for someone else, think about the simple idea behind it. Not everyone knows what your image is about. Make things simpler and they would appreciate you for adding an image caption. Got it? Now let's take a look at how you can add an image caption for images in Blogger.
1. First off, you need to have the image added to your post or page.
2. Click on the specific image in Post Editor which you wanna add image caption.
3. Now you will see image options panel beneath the image and click Add caption there.
5. You just have to erase default image caption and enter your desired image caption for the image.