When we drag mouse over the image it displays name.I don't know how the browser shows the name.The name based on what?Name in the alt attribute or name in the title.
The reply here has a good writeup of what each is for:
ALT tag is an accessibility tag that was introduced for people who have sight difficulties even through Google use it to determine what an image is about you should never consider putting alt tags for SEO purposes before your visitors.
The title tag was designed to give more information when you hover over an element, its not very useful for IMG because if you intend to use the same information for ALT and TITLE then you can use a script to read the alt tag and make your very own hover overs using JS. I would only recommend the title tag if your going to provide more information than that of the ALT tag, like a longer description - no need to provide the exact information in both elements, as that just bloats the code.
Google "image alt vs title" for more information.
when you hover on an image the text you see is the title
the alt text is shown if the image is not showing