Size matters, it matters a great deal when it comes to websites. The larger an image, the slower it will take your website to load, the less kindly Google will look upon it for top page rankings. And then multiple that by many images and the problem increases sizeably (excuse the pun).
There are lots of easy fixes to overcoming larges images and optimising your pics to the smallest size without compromising on quality. Here are just a few tips and tricks that are used extensively at Spoonful...
Shrink O'Matic - this free, tool (that you install locally) allows you to optimise your jpg images. It's so simple to use and can reduce your images up to 90%.
Tiny PNG - also free but is used online, this tool optimises your png images. This is especially good for transparent images, which must be saved in PNG 24 for best quality. This tool is available as a plugin for Photoshop for a small cost.
GIMP for Images Editing - an ideal, free, alternative to the expensive Photoshop. This is great for manipulation of photos and also optimisation.