Adding descriptive Titles to your images, and/or specific strings of text within your content, will greatly increase your SEO (Search Engine Optimisation). If you name your images with an exact string that you might expect someone to “Google”, your image (and your website) will then rank highly in any Google results. Making the Title specific, but also unique will give excellent results. For example, if you were to name an image “twitter free zone”, then anyone Googling twitter free zone would quickly find your website. Your challenge is to predict what people will be Googling (exact string), then include an image you can name accordingly. The more correctly named images you have, the higher the Google ranking for those strings will be. Do NOT try and trick Google by adding excessive images with blatant SEO Titles, Google will recognise that and blacklist your website completely. Just include relevant content, with relevant images with descriptive titles, and Google will love you, and people will find you.
Updating/adding relevant content to your website, through images, documents, videos, text, etc will increase your Google ranking. Google visits and indexes your site periodically, automatically. If nothing has changed when Google comes back, the period until the next visit will increase, each time. That is how your Google ranking drops. To maintain or increase your Google ranking you must keep an active, relevant website.
Please see also Website title and SEO article.