I've tried to use intermediate images but: 1) GD gives me the typical memory allocation problems and I can't modify php.ini 2) I want that every user in my site can upload images... so intermediate images won't work for me.
I've been using the search these last 2 days for an alternative, but didn't find what I have in mind (maybe I didn't use the appropiate word!). What I need is to display the image shrunk if its width (not height) is over 800px. Then, if an image have e.g. a resolution of 1000x500, it would show the same image but with img params: width=800 and height=400 (in proportion). I don't know how to modify displayimage.php to achieve this.
Thanks for your support, and sorry for my english.
Coppermine should do exactly what you're up to if you set "Create intermediate pictures" to "no" in Coppermine's config.