The SearchPreview add-on includes a few customization options, like limiting the maximum number of returned images one a page, and including popularity rankings. In our tests, SearchPreview is accurate and didn't hinder performance. It does sprinkle sponsored links into the search results from time to time, a behavior you can nullify in the settings. A feature that magnifies the thumbnail size from the search results page would be a welcome improvement in future releases. SearchPreview isn't essential for searching, but it certainly comes in handy.