Not really, no.

Meta data will influence how you are classified. Choosing the right keywords is important.
Too many people have abused keywords, and search engines now try to get a better classification system.
Therefore, the robots now also check your page to find whether the content actually matches those keywords. They have to do this by checking the text.
So if you use images, it's best to also have text. Not only as alt and title inside the img tag, but also in just plain text. This text you can either hide (as explained above) or project into outer space by setting a margin left or right of, say, 9000pixels.

But it is not obligatory. It only helps you up in the rating, and into the first pages rather than at the bottom of the last one.

There are no Borg. All resistance is fertile.