For various reasons, including SEO (search engine optimization) and usability, we encourage web authors to consider the following when naming images and files:
Be sure to keep image file names in mind also. Never use the default filename assigned to an image by a digital camera. Ex. WIN_0011.JPG, _DSC0015.JPG, IMG_2204.JPG, and the like. Use logical words for naming images. Doing so will help with SEO and usability. In regards to SEO, by providing search engines with textual information for images, your site will benefit from both better placement in search returns and improved positioning in image search results. Remember to use hyphens rather than underscores to separate words.