Let's take a simple example:

x = 1
[= x plus 1]

We've set x equal to 1 and then we've asked it to interpret the phrase "x plus 1". I've used the notation "[= x plus 1]" to mean "ask for a natural language interpretation of x plus 1".

If you evaluate this, you'll see that it returns "x + 1" and not "2". Once we evaluate "x + 1" though, it will return "2". The value of x is not part of the natural language processing. Instead, the natural langauge processing returns and expression with "x" in it and that value of "x" is substituted locally with the value of "1". The distinction is important to understand if you are using variables like this.

The NLP functionality doesn't seem to handle much image processing at this time. You might try looking at some examples of this with Wolfram|Alpha.