When a site has a favicon.ico file in its root directory, browsesrs fetch it and display it as an indentity mark, particularly on the page's tab. A .ico file can support multiple sizes of image. For professional sites, each size is created by an artist. For physpics, the default is to supply one large image in /images/logos/favicon.png. From that, the page Makefile derives images of size 16, 32, 64, and 256. All of which it combines into favicon.ico and copies to /favicon.ico. In addition it creates file /apple-touch-icon.png (256x256) and copy it also to /.

The default original image (favicon.png) is a 256x256 version of the writing hand (✍).

To produce other sizes of favicon or apple-touch-icon, just name them in COPYFILES, say favaicon48.png or apple-touch-icon-140.png.

Icons for the pictools distribution have been manually preconstructed. The necessary Makefile rules are distributed from pictools/forSRCROOT/images/logos/Makefile. The main rules are

# favicon.ico encloses four sizes of image
favicon.ico:  favicon16.png favicon32.png \
                        favicon64.png favicon256.png 
	convert $^ -alpha off -colors 256 $@
favicon%.png: favicon.png 
	convert $< -scale $*x$*! $@ 

The first rule depends on having one image in each of four sizes and then combines those images into a single .ico file. The second rules converts favicon.png into a version of a particular size.