Uploading Images Resize

Uploading Images Resize

I have a huge image that is going to be uploaded to my server. The width
and height are for example: 2000x2000. I have multiple places in my code
where I need the image to be 1000x1000, 250 x 110 or like 100 x 50. When
they upload the image, should I make ASP automatically re size to these
dimensions and save them on my webserver like image-250x110,
image-1000x1000, image-original, and image-100x50 or is it fine to just to
get the original image and re size on the fly through the code then show
it to the users. I'm asking this because I'm worried that if too many
people go on your website, re sizing the original huge image all the time
would take alot of processing power and slow down the app. Or would
something like this would be fine:
http://www.hanselman.com/blog/NuGetPackageOfWeek11ImageResizerEnablesCleanClearImageResizingInASPNET.aspx