calling an html input in c# code behind

I have an html input on my aspx page. I have code behind that needs to call it and cant figure out how. any suggestions?
I am getting the error for "Posted File"
"does not exist in current context"
//////////////////////////////////////////////////
<input id="uploadFile1" type="file" name="image" class="img" />

if (uploadFile1.PostedFile == null || string.IsNullOrEmpty(uploadFile1.PostedFile.FileName) || uploadFile1.PostedFile.InputStream == null) { return; }