For most of us its complicated to say if image alt attribute or title attribute is more important for the SEO of page and how to go about adding these two elements in images.
The ALT attribute
Alt is a short text to describe an image when it fails to appear on the page. This is important in situations where internet connectivity is slower or image isn’t showing up due to some reason (deleted or failed loading). In such cases, alt text appears in place of the missing image and hence doesn’t hampers readers in understanding the textual content around it.
Search engines know little about the images hence they read alt text to understand the image while crawling.
Thus, alt attribute is important in terms of SEO of a page. Google confirms it in its blogpost on Google Webmasters Blog. Here is a video by Google’s Matt Cutts explaining the same,
The TITLE attribute
Title of an image is same as the title of any textual content (or heading of this post). Its for providing additional information and appear only when cursor is moved over it. Like alt, title information should be relevant, informative and must not be lengthy.
Title has no value to search engines. So adding them is optional.
1. Adding alt text is important for SEO as search engines takes them into account while crawling a webpage. It must be short, relevant and keyword-rich.
2. Adding title text is optional as search engines don’t consider them at all, and readers can’t see them without hovering the image.
3. If both are includes, image title and alt text should be different from each other. If both are same it may lead to keyword stuffing which is fatal for websites as search engine discourages it.