Just some quick comments

1) As Klaus and others have explained several times.
For the current browsers the DPI setting of bitmaps on a web page is irrelevant, even for bitmap file formats, such as JPEG, which have DPI info ( a GIF file does not have DPI info, it does have info for the number of pixels x&y, colour depth etc ). Browsers IGNORE DPI information, they will render the image according to the number of pixels in the image. So for the moment one could justifiably say that the DPI is completely and utterly irrelevant to web designers.
All the photoshop stuff suggesting you set the DPI to 72 is irrelevant if this info is not stored in the file format! It is relevant if you wish to PRINT a JPEG image, but photoshop is not to know that user is going to use a JPEG for the web only, so it will suggest setting the dpi to 72.

2) I have a pet theory that one day in the future browsers will NOT ignore this DPI information and will provide a zoom on to a page facility. When this happens web pages will be able to include high resolution bitmaps AND control the size of these images, this is what DPI control gives you. With this control a designer could place what would appear to be a dot on a web page, that, when magnified by altering the zoom setting of the browser window, would reveal a full resolution photograph. So thumbnails, and the like, would be a thing of the past, hi-res images would appear at a small thumbnail size and the user would use the zoom facility of a browser to see the fully detailed image. Of course, this would require all viewers to have high bandwidth web access to download the vast images quickly, but this will be coming soon.

3) There is an alternative to placing DPI information in the image and still achieve the behaviour described in 2). HTML provides the web page designer with control over the dimensions of the image irrespective of the number of pixels in the image, this is done with the width and height properties of the image tag. This, in effect, provides resolution control, as the width and height can be defined in mm, cms, as well as pixels. ( Though I don't think current browsers respect these units because, as we know, this requires the browser to know the physical dimensions of the monitor screen, 14", 20ft ?, so some sort of standard would be required, perhaps a new unit? )

4) What will we do when monitors have 10000*10000 pixels?
We will then have to include resolution information in images or in the HTML to ensure that the images and pages don't appear as tiny dots to the user at 100%. The current behaviour of browsers ignoring DPI information is just a result of the low resolution of the output device ( the monitor ).
When this time comes Klaus will have to explain at length why resolution information is important or why the units for width and height have to be a in a strange new unit.

Mark Goodall
Xara Ltd

[This message was edited by Mark Goodall on December 12, 2001 at 04:27.]