When it comes to bringing search engine traffic to blogs, images do that. Search terms ie. keywords people type into search engines can result in traffic to your images as well as to your posts. That’s why learning how to optimize images for Google search is an important skill for bloggers to acquire.
All images ought to be optimized and re-sized prior to uploading them into your blog. When you decrease the file size for images before you insert them into your blog, uploads and pages will load faster, you can fit more images into the same space, and using the correct tools means you will not compromise the quality of the image.
Before you upload your image, optimize and pre-size it, and give it a descriptive file name including a keyword. Stick to letters and numbers only and be sure that the image file type is one of these .jpg/.jpeg .gif .png
The Google crawler cannot read image scripts and therefore using the Alternate text ALT attribute (providing a concise text description) will allow you to tell the crawler what the image is referring to. If you want your images to be indexed then give your images the full treatment. While creating a post or page on your WordPress blog, when you insert an image within the post you have an opportunity to complete all these fields:
Without a TITLE tag, no ‘hover text’ will show up when the mouse passes over your image. Hover text is a useful way of letting search engines and readers know what’s in a picture. Include a keyword in title.
Alternate text (ALT) attribute is for situations when an image cannot be loaded and also assists visually impaired people who use apps to read ALTattribute, so what’s in a picture is known.
According to the W3C recommendations, the ALT attribute specifies an alternate text for user agents that cannot display images, forms or applets. The “title” attribute is a bit different: it “offers advisory information about the element for which it is set.”
Why not be as descriptive as possible? The Description will appear on the permalink page of the image in the Media Library. If your uploaded image is used in a Gallery, the Description will appear on the Attachment page.
When people view images, their eyes naturally drift down and captions display directly below the image.
This is the location of your image. Take note that it cannot be modified.
Matt Cutts Discusses the Importance of ALT Tags
Additional SEO tips for image optimization
Out of all the testing we did our JPG images always performed the best, this is probably due to the fact they are the most common and can be read by all browsers. Plus you can easily compress them reducing load time on image heavy pages. We try and stick to between 1KB and 60KB for all our images, anything over 70KB tends to take too long to load and never performs as well. — Getting the Most Out of Image Search, More Links & More Traffic