Secure file upload

Hi everybody, this is my first post.

I'm actually working on an asp.net web site wich includes an upload file control. My site should only allow images to load, I have client and server side validation of file extension. The real problem is when the image is displayed, it wouldn't be too hard for someone to change the file extension of a file so it would be accepted and uploaded to the server, thereby bypassing the security.

So, there is a way I could read the file header and verify the file is being upload is really a image file? or is there another way to face this problem.

By the way, the file is saved to a sql server image field.

Any help would be appreciate.

Thanks in advance.
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