image resizing

[JJ]

When inserting new articles on my site users can populate one field with an
image url.

when the user then clicks on the submit button to add the article (body
field and a seperate image url field), I want to be able to resize the
images, keeping their ratio, so that the image is displayed within the
maximum height/width restrictions.

I understnad that just changing the height & width parameters of the img tag
just leads to bad quality images. I guess I need to actually resize the
original image and clear any height/width parameters in the img tag that the
user may have input. However I am a little confused as to how to do this.

Can anyone point me to any code/examples - preferably in c# ?

Many thanks,

JJ