Settings for web-size files?

[filemanager]

My web-size files are 500px are the longest side (though I'm thinking about changing that to 400px).. but I've been playing around with some things.

If I take a 500px (72dpi) file, and open it in Photoshop and simply change the image size to 2000px - the quality doesn't diminish that much.. so if someone buys a low-res file like that they could (if they had the knowledge) upsize it themselves and print englargmenets, couldn't they?

(If I save that same file with a "Quality" of 3, then when enlarged the picture becomes very distorted and they wouldn't be able to do that.)

I was just wondering for those of you who do web-sized files, what the settings that you use are?

[Jim Bryant]

450 on the long side. DPI 72 and save at quality 3 or 4.