How to check the content of an uploaded file without relying on its extension?

Question

How do you go about verifying the type of an uploaded file reliably without using the extension? I\'m guessing that you have to examine the header / read some of the bytes,

Answer 1

Here's a quick-and-dirty response to the followup question you posted:

byte[] jpg = new byte[] { 0xFF, 0xD8, 0xFF, 0xE0 };
bool match = true;
for (int i = 0; i < jpg.Length; i++)
{
    if (jpg[i] != b[i])
    {
        match = false;
        break;
    }
}