I was having a similar issue, and I have discovered that the UIWebView elements in IOS do not support the html element:
<input type="file">
I am not sure why Apple chose to not support this IMPORTANT html element, but I am sure they have their reasons. (Even though this element works perfectly on Safari on IOS.)
In many cases, when the user clicks this kind of button in a UIWebView, it will let them take/ choose a photo. HOWEVER, the UIWebView in IOS does not have the capability to attach files like this into the POST data when the form is submitted.
The Solution: To accomplish the same task you can create a similar form in InterfaceBuilder with a button that triggers the UIImagePickerController. Then, you create you an HTTP POST request with all of the form data and the image. It isn't as hard as it sounds, check out the link below for some sample code that gets the job done:
ios Upload Image and Text using HTTP POST