Image labels are such a minor detail to a website that no one really thinks about them. However, it is very important to label the images throughout your website.
This needs to be done because of the different speeds of internet connections. If someone has a slower connection to the internet that means that your website is going to load at a slower rate for them. Images typically tend to be the last items on a page to load. The viewer is going to see a box with a red x at first if the image is loaded incorrectly or not properly labeled. Not to mention that a red x would also been seen if your website was not properly formatted to the browser that the visitor was viewing your site in.
So now that you know they are important, how do you label them? To label the images you need to change the alt tags to be text that describes the image. Remember, the text that you write is what is going to show when an image can not be displayed. For this reason, the text needs to be as descriptive as possible, yet concise.