Can an image be redacted, or just text?

Looking at the definition for redact, it sounds as if it specifically applies to text. Can it be used with images and diagrams as well?

If you don't specify what to redact, a listener might assume you mean to sanitize a document or black out text. There's a strong association with text, but it doesn't mean you can't use the word "redact" with other things.

The current use of redact often includes image redaction, especially when discussing electronic files such as Word or PDF documents.

The NSA Redacting with Confidence guide (note, 1.4MB PDF available from NSA index) discusses redacting images - for example:

Select each chart, diagram, image, or segment of text to be redacted and delete that item.

Adobe PDF tutorials also address this issue with phrases like:

Redacting text and images in a PDF file

So if you say

We should redact the diagram on this page.

you'll be understood.

Note: Redaction has a specific meaning in literature. I'm assuming you're talking about the document sanitization meaning.

While you might be understood when using it in a different context, it is generally recognized as referring to a process that is only performed on a text.