Web browsers, at least those with which I am familiar (Firefox, Opera, Internet Explorer, Mozilla, Mozilla Seamonkey), allow their users to save individual web pages onto their hard drives, complete with all images.
If you’re using Firefox, you can do "File, Save Page as Web Page (complete)" to save the complete page.
The pages HTML is stored in the directory you specify. However, everything else that this page pulls from the web (counters, jpg images, gif images, png images, etc) are stored in the subdirectory of the same name as you assign when you save the web page. Then, also within that directory are additional folders for any inline frames (iframes).
When I used Firefox to save the article http://trekmovie.com/2006/08/28/star-trek-tos-gets-redone-with-new-cgi/ on the reworking of Star Trek, it created 6 subdirectories in the main subdirectory, one for each of the iframes used by the Amazon.com product ads.
Internet Explorer has a similar function (you choose “Save As Web Page”) but doesn’t create as many subdirectories of the main subdirectory in this particular case.
All the text content is contained in the main page, while the subdirectory has all the images.
If you delete the subdirectories, you’ll lose all the images. Then, if you try to display the page, you will either get the dreaded "Red X" (in IE; other web browsers also indicate missing images) or the lack of images could totally mess up the formatting.
If the web designer specified the sizes of the images, the page will display normally. However, since web browsers will automatically determine the correct size from the images built-in data, many web designers don’t do this. Internet Explorer will show the Red X, if the web designer did not use an Alt tag to describe the image. Other browsers have other indications of missing images. All will show the image’s Alt tag, if available, in place of the missing image.