Dashes or underscore for image names?

I usually ask myself the same question when I try to name an image. Should I use dashes or should I use underscore?

So I use Google search engine and find 2 good articles about this topic. Both recommend using dashes.

• http://www.mattcutts.com/blog/dashes-vs-underscores/
• http://themetaq.com/articles/seo-under-scrutiny-are-hyphens-or-underscores-better-word-separators