how can we crop a image in web page

It depends what you mean by crop. If you really mean resize, then just set the size of the img element. If you actually mean to extract a portion of the image, then you can do it before the image is rendered. Something like this;

Bitmap bmp = new Bitmap(existingImage);
Bitmap bmpCrop = bmpImage.Clone(croppedArea, bmp.PixelFormat);
return (Image)(bmpCrop); 

Try this[^] link it will definitely help you.

You can use the JavaScript Image Cropper UI to solve the problem. Following is the example for ASP.net and C#.
ASP.NET Image / Photo Cropper in C#

Hope this[^] might help you.