PHP move_uploaded_file permission denied (permission set to 755)

I'm trying to upload a user's photo using a simple HTML input form, but I'm getting the following error. I've set the permissions of my upload folder to 755. I tried 777 and that works, but I've read that setting it to 777 is not advised and that I should be able to use 755?

Warning: move_uploaded_file(uploads/2014_08_21_11_03_14k.jpg) [function.move-uploaded-file]: failed to open stream: Permission denied in /home/yadayada/register.php on line 136
Warning: move_uploaded_file() [function.move-uploaded-file]: Unable to move '/tmp/php8KQwyh' to 'uploads/2014_08_21_11_03_14k.jpg' in /home/yadayada/register.php on line 136

This is my php code:

$userPhotoUrl = 'uploads/'.date('Y_m_d_H_i_s').$_FILES['photo']['name'];

if (is_uploaded_file($_FILES['photo']['tmp_name'])) {
    if (!move_uploaded_file($_FILES['photo']['tmp_name'], $userPhotoUrl)) {
        // show error message
        return;
    }
} else {
    // show error message
    return;
}

Solution

First of all, you have to understand what is 755.

For folder, 755 means drwxr-xr-x, which means:

Owner has Read, Write & Execute permission
Group & Public have Read and Execute permission only

As the user running PHP is probably not the owner of the folder, it does not have write permission to the folder. Either:

You chown the folder to PHP's user; or
You make it 777: everybody has Read, Write & Execute permission

Of course, the latter choice has a security issue, as if somebody uploads an executable shell script to your folder, he can execute the script. Therefore, you should stick with the first choice.