OK, after much research, I've answered my own question and come to the conclusion that this can't be done in IE8.
The solution that I thought would be most viable would be to load the image into a hidden DIV on the page and then grab it using a third party plugin before posting it to the server using AJAX. And this method DOES seem possible - but not using IE8.
There's a very useful library called HTML2Canvas which does exactly that, using the 'canvas' element of HTML5 - but of course, this only works on other browsers like FF and Safari, and IE versions of 9 or above. As seen on the examples page here, the library gives an "Object doesn't support this property or method" when run through IE8:
http://html2canvas.hertzen.com[
^]
There are apparently ways around this, as there are other libraries out there that successfully emulate the same canvas functionailty in IE8 - most notably Google's 'Explorer Canvas', and also 'FlashCanvas'. But while these both provide the majority of functions you get with a normal HTML5 canvas, they do not provide the critical function required called 'toDataURL' - which allows you to grab the canvas from the screen. Even though FlashCanvas now claims to support this function, having tried it for several hours I'm convinced that this cannot be used with HTML2Canvas for the purpose I need it for.
Having browsed around on other forums, it seems that other people are also having problems trying to get this solution working, and so for now I'll have to rule it out and devise some other way round it. Hopefully this might be of some use to anyone else attempting the same thing.
Cheers
Nick
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