Pictures in websites are great and often make a page. There is an increasing trend to have a high resolution picture filling the frame. Looks brilliant. But care is needed.
A large picture that fills the frame can easily be four megabytes in size. In internet terms that is big and could have a real impact on how long a page takes to load. It isn't just the big pictures that can present a problem though. If you manage your own website maybe using WordPress or the like, have you considered the size of the image you are uploading to your page. I know you can change the size it appears on the page but that doesn't effect the actual file size. To fix that you need to change the size, pixels by pixels, on your computer before you upload it. Most images are saved as Jpegs. This means you can compress the image and make it smaller. Again this needs to be done on your computer before uploading it.
I find many people don't have the time or the interest to 'mess around' resizing their pictures. A solution to this is a script on the website that resizes the actual picture on the website based on the display size you have set. This works when someone visits the website and views the picture the script quickly resaves the image to the right size then displays a resized copy of it, or a cached version. This only happens once so it's only the first user that experiences a slight delay in the picture being shown. I generally like to check a new page or image so that would be enough to generate the cached or rezized image.