
Image Tags, are a really important part of Search engine marketing, it's just another way to tell the search engines what your website is all about...
The most efficient way to get google on your side is to make your website predictable, if you name your page, content and meta tags about one thing, the last thing you want to do is to name your pictures something that has nothing to do with your page content, sure... you can leave them blank! But at the same time why not reinforce the information you have already, one important factor, or something to watch, when you save your image file after manipulating it in the photo editing program, save the file relevant to what it is.
If its a spade, call the file spade 1.jpg or something similar, the reason for this is: When you load the image onto the website, the search engines can see the original file name, so one way for it to believe your alt tag, is to look at the relationship between the original file name and the alt tag.
When you place the image on your website, put something descriptive in the alt tag, this is the small box that appears beside the picture when the mouse runs over it, in the alt tag put: spade with red shaft and blue handle. the reason for such a good basic description, as you probably know the the big search engines like your website if it is user friendly, well...you have to remember not everyone has great eyes sight, some people with poor eyesight will normally be running a special web program that describes the the web pages and alt tags.