All good advice here and I’m just going to add one thing.
Besides resizing your images, it’s a really good idea to compress them, especially since you are using so many of them.
Best, fastest way to compress that I know is to use a free tool called tinypng.com
just upload the image from you desktop (where it should be, for reasons Jennifer gave)…
then compress and download.
The image SIZE remains the same as does the pixelation… it looks the same but is much much smaller.
This makes your site and pages load much faster, and greatly reduces your bandwidth.
Not a big deal for casual bloggers, maybe, but certain for an ecom style site it is.