You should saved resized image along with original image after upload complete.
Say you would save uploaded image in Images/UserImages
then you can save uploaded image's resized version in Images/Thumbnails
. You can resize image to whatever size you want; there are number of articles in codeproject for that.
After that you can write html as
<img src='/Images/Thumbnail/MyImage.jpg" />
So clicking on thumbnail will redirect you to image path from where you can get original size image.