Could any one please let me know applying keywords to alt tags for images is white hat technique or black hat technique?..... Immediate replies are appreciated....
Well, in google webmaster guidelines nothing is mentioned about prohibition of alt tag. So you can definitely use it, but it would not give you that much increase. Moreover, this tag is useful for your visitors who have disabled showing pictures in their browsers.
Matt Cutts from Google encourages the use of ALT tags in many videos on Youtube, check them out! Make sure they describe the image and are not just stuffed with keywords. If your main heading is an image then wrap <h1> around it and use the ALT text to say what the image says.