1. Name of Picture File: Google look at the file names of the images, specially in the Google image search.
2. By adding perfect Alt Text to the images.
3. Sharing images to the sites like Pinterest, Piccassa, Flickr and more.. with proper webpage link and description
4. Image Compression using Smush.it Plugin
5. Social Media Activity:
You should optmize images on your website with appropriate alt text, description, title tag etc, also you should promote your site on social media sites like pinterest, clipix, clipboard, we heart it, fancy, gentlemint etc.