Images are page signals and factors of many...
Images always help because they are one of many signals using the ALT to inform Google what the page is about, however to say they are needed is also false, its one of many factors. Google can establish factors from many other signals such as TITLE, Meta, Content and so on.
Write content for your visitors not the search engines...
You should always write content for your site visitors, writing and adding content merely to satisfy search engines is the worst seo because your defeating the objective, site visitors not search rankings. Ultimately more visitors and more returning visitors you higher your chances for social mentions, back links and other PR exposure which is by far the best SEO and long term strategy you can do.
Summary
Images are not needed to rank pages as they are one of many page signals. The only thing negative about not having pictures is that you miss out on traffic that can come from Google image search but again you should only ever use images on your site to please your site visitors not search bots.