<form enctype="multipart/form-data" method="POST" action="ads.php" />
Name:<input type="text" name ="name" /><br />
Book:<input type="text" name ="book" /><br />
Subject:<input type="text" name ="subject" /><br />
Price (CAN):<input type="text" name ="price" /><br />
Description: <br /><textarea cols="40" rows="5" name="description">

</textarea><br />
Click to upload:<input type="file" name="pix" /><br />
<input type="submit" name="Upload" value="Upload Picture" />
</form>

I want this form to only submit if the pictures are either gif, jpeg, or png.

I want to have protection against blank entries, incomplete entries. duplicate entries

Would that require an IF statement? Or something more advanced like JQuery / AJAX?