One fascinating aspect of HTML is the fact that a web page written for a web browser released 19 years ago will still display fine (pages designed for later browser are much more of a problem). Today we take the ability to have images within a web page for granted, but it was the big innovation of the Mosaic web browser. The tag for inserting images into web-pages was proposed in a simple e-mail from Marc Andreessen:
Required argument is SRC="url".
This names a bitmap or pixmap file for the browser to attempt to pull over the network and interpret as an image, to be embedded in the text at the point of the tag’s occurrence.
An example is:
(There is no closing tag; this is just a standalone tag.)
This tag can be embedded in an anchor like anything else; when that happens, it becomes an icon that’s sensitive to activation just like a regular text anchor.
Browsers should be afforded flexibility as to which image formats they support. Xbm and Xpm are good ones to support, for example. If a browser cannot interpret a given format, it can do whatever it wants instead (X Mosaic will pop up a default bitmap as a placeholder).
While the tag was universally adopted, the image formats he suggested were not. No browser I know of supports XPM images, and XBM support is far from universal. If you do not see an image in this post, your browser does not support XBM. This made me curious, so I created a small image test page, it contains the same image (the Telefunken PAL test pattern) in various formats. The image range from esoteric formats like Targa, to old workhorses like Tiff to the newest proposals like WebP. As far as I know, no browser manages to display all the images.