There are plenty of software packages around that will generate images that you can save and then incorporate into your web pages. Here is but a small sample:
import lets you capture
window from the screen into a file. Give the command
import -frame file.giffile.gif.
The cursor will turn to a crosshair,
and you then click on the window you want to save. Be sure
the window is not obscured by other windows. Omit the
-frame option if you don't want the window
frame (border and titlebar) saved.
To capture the entire screen, use the command
import -window root file.gif
Note that import is rather slow; it may
take a minute or so to do its thing.
On SGI workstations there is a program called
snapshot which you can use to capture a region
of the screen which you select with the mouse. See its
man
page for details.
When using Netscape and viewing a Web page that contains an image, you can put the mouse cursor over the image and press the right mouse button to bring up a menu which will let you save the image to a file. (On a Mac, hold down the Option key and press the single mouse button.) Other browsers may have similar options.
You can also fetch an image by specifying its URL directly,
for example http://www.geom.umn.edu/pix/welcome.gif.
(This method works for fetching background images as well; use the View Source option of your browser to look at the html source for the document to discover the file pathname of the background image.)
The Geometry Center has a scanner attached to a Macintosh; you are welcome to use if whenever you're in the neighborhood... Otherwise, you'll have to locate such resources at your own site.