XML? was: a tithe of links.

A question in view of the numerous concerns expressed regarding
bandwidth taken up by graphics:

Is it currently possible to link to the local hard-drive and use a local
graphic if present, possibly with the option to download alternative
graphics*?

I am not certain about the following, but given that many sites
including wai use a graphic repeatedly, is this already part of html? If
so how does one simply ensure that the local graphic, if available was
linked to?

---

*A possible way to identify graphics uniquely* is to take a diagonal
line through the field eg a 32x32 2 bit image might have the code
10001010010011001110000110110100. Which could be in the header, or in
the html.

*A colleague in another field devised a simple and fairly successful
means for identifying 'GO' games.

-- 

jonathan chetwynd
jc@signbrowser.org.uk
IT teacher (learning difficulties) 
& accessibility consultant