Google can not 'see' images, but it can read all it's properties and can therefore use them to establish rankings for pages with images. First of all, you should therefore start with images with relevant names. If you use an image about an Ipad, name it ipad.jpg or something similar, as long as it contains the word ipad. You can even use multiple words, if you use dashes or underscores to connet them.
Secondly, when inserting an image, you should enter an alt-tag. You can easliy achieve his with most editors. Both TinyMCE and JCE have options to enter alternate text:
JCE even does this automatically by filling in the file name without extension, so if your file name is correct, you very easily have your alt-tags right. Of course you can still write your own.
Besides being good for SEO, it is also good for accesibility for disabled users that use screen readers. When you want to verify you did this process in a correct way, you can run your site through the www.feedthebot.com/tools/alt website.
When looking at images, also make sure to reduce image size as musch as possible.