When it comes to on-site optimisation, images are one of the most missed opportunities and one which many website owners get completely wrong with regards to SEO. What you need to be aware of is that when Google crawls a website, its spiders do not see images, only text.
For example, if you were a local dog groomer, and had an image of a beautifully groomed German Shepherd on your website as an illustration of your great grooming skills, if that image file was simply called ‘image1’, that is what Google takes it to be; image number 1. It doesn’t see a German Shepherd; in fact, it doesn’t see a dog at all.
Now, if you name the image file ‘German-Shepherd’ and upload it to your website, Google will see those words, and better still is if you utilise the alt-text function. Alt-text is what you might see on your screen if your mouse hovers over an image, but more importantly, it is what Google’s spiders send back when they come across an image.