getimage: Details
Operation
getimage is a cgi-bin program that is called by a webserver. It looks for GL_IMAGE_ID in the QUERY_STRING environment variable, associated with http GET requests. It retrieves a file number from GL_IMAGE_ID value, and puts together a filename that is a constant string plus the number. It then opens up the GIF file and reads in the contents, and closes it. It then sends some header information back to the webserver identifying the content type, followed by the contents of the GIF file. When it is done sending the data, it deletes the GIF file.
If anything goes wrong along the way, it will dump an error message back to the webserver, and the web-client will get a broken picture icon in their browser.
Images Don't Get Deleted
If you have one or more web based programs running that generate dynamic gifs(maps, record sections), then you may eventually get overrun by old images. Under perfect circumstances, someone loads a webpage that creates a dynamic GIF, the program that generates the webpage runs and produces the web page as well as a GIF. Part of that webpage is a link to getimage. The browser receives the webpage, and makes another request to getimage in order to retrieve the image. getimage is called, it dumps the image back to the client, and then deletes it. The client gets their dynamic webpage, and the server is none the worse.
However, sometimes things go awry. The web user changes their mind and cancels the web request partway through, or there is a network problem, or it takes too long to wait for the page, so they hit ReLoad. The first program may complete, and so the dynamic GIF is created, but since the web browser never receives the finished page and never requests the image from getimage, getimage never gets called and the file never gets deleted. This happens a lot, and so you may need to implement an automated backup scheme for deleting old images.
Potential Bug on NT
This program may not work on NT with older versions of Apache or Netscape Fasttrack. The webserver opens up a pipe from the stdout of the cgi-bin program(this one) to the webserver. On NT, that pipe was getting opened in "text" mode, which meant that everytime the pipe saw a bare linefeed without a carriage return, it would add a carriage return. This causes problems with GIFs and other binary files. You can call _setmode() as in below, to force stdout to binary mode, if you wish to use this program with older versions of webservers on NT. (Solution found by cjbryan).

        result = _setmode( _fileno( stdout ), _O_BINARY );