CSS for Text Over Image in Blog Post?

There’s one thing I want to do that I can’t find in these forums: have white text appearing over an image. And, making the said image go darker so that the text stands out. Like this:

Is there a way to do this in a post on Write.as?

Of course, I could try to do it as a static image (using a graphics program to write the text into the picture), but it’s preferable to do it with text over the image via CSS because then the word wrapping will adapt to the screen width of the device. And, the text will be picked up by Google, so better SEO.