Field Authentication

I am back. And slowly learning... slowly...

I have a form where I need to do three things.
1. Check for blank fields
2. Upload an image (I can deal with this one)
3. Check to see if a field contains specific information (IE a password)

Code:

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        <form id="photoUpload" enctype="multipart/form-data" onsubmit="return check(this);" runat="server">
                        <fieldset>
                                <legend>Share your pictures with us</legend>
                                <p align="right"><label for="fname">First Name<em>*</em></label>
                                        <input id="fname" /></p>
                                <p align="right"><label for="lname">Last Name<em>*</em></label>
                                        <input id="lname" /></p>
                                <p align="right">
                                <label for="fulPhoto">Upload your image</label>
                                        <input id="fulPhoto" type="file" runat="server"/></p>
                                <p align="right">
                                <label for="thbPhoto">Upload your image</label>
                                        <input id="thbPhoto" type="file" runat="server"/></p>
                                <p><label for="password">Password<em>*</em></label>
                                        <input id="password" type="password" /></p>
                                       
                        <div class="btn" id="thbUpload" style="padding-top:4px">
                                        <input id="btnUpload" type="button" value="Upload Photo" onclick="passwordBox()" />
                        </div>
                        </fieldset>
        </form>

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There is the existing code and I have a small function that is checking for the blank fields and that I would like to change to check for the correct password....

Code:

---

//function to check empty fields
function isEmpty(strfield1, strfield2, strfield3) {

//change "field1, field2 and field3" to your field names
strfield1 = document.forms[0].fname.value
strfield2 = document.forms[0].lname.value
strfield3 = document.forms[0].password.value

  //first name field
    if (strfield1 == "" || strfield1 == null || !isNaN(strfield1) || strfield1.charAt(0) == ' ')
    {
    alert("Your full name is required please enter and try again")
    return false;
    }

  //last name field
    if (strfield2 == "" || strfield2 == null || strfield2.charAt(0) == ' ')
    {
    alert("Your full name is required please enter and try again")
    return false;
    }

  //password field
    if (strfield3 == "" || strfield3 == null || strfield3.charAt(0) == ' ')
    {
    alert("A password is required to upload your photos please try again or contact us to obtain a password")
    return false;
    }
    return true;
}

//function that performs all functions, defined in the onsubmit event handler

function check(photoUpload)){
if (isEmpty(form.fname)){
  if (isEmpty(form.lname)){
    if (isEmpty(form.password)){
          }
  }
}
return false;
}

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But.... it doesn't work. And I don't know what I did wrong. Well I am sure numerous things but specifically, no idea. Thanks in advance.