upload image to the database with wordpress (plugin)?

I am doing a plugin for wordpress a CRUD and I have decided in my form to add a input type file to upload images (which I only want to save the path of the image only once moved to my server)

<form method="POST" ENCTYPE="multipart/form-data">
<input type="text" name="Nombre" value="<?php echo $name; ?>" class="ss-field-width" />
<input type="file" name="img" value="<?php echo $img; ?>" class="ss-field-width" />
<input type='submit' name="insert" value='Guardar' class='button'>
</form>

and it turns out that when sending the data the variables using $_FILE[] arrive empty but those that you have $_POST[] if I get the information

 $imgname=$_FILES["img"]["name"];
 $tipo_imagen=$_FILES["img"]["type"];
 $tamagno_imagen=$_FILES["img"]["size"];
 $tmp=$_FILES["img"]["tmp_name"];

and that does not allow me to put the data into my database (which I'm using global $wpdb; to insert my data)

global $wpdb;
$table_name = $wpdb->prefix . "mitabla";
 $wpdb->insert(
        $table_name, //table
        array(
            'img'=>$imgname
            ), //data
        array('%s', '%s') //data format
);

which in my form using the enctype="multipart/form-data" I get the data to my $_FILE but I do not insert it into my database, but if I remove it from my form the enctype="multipart/form-data" I get all empty fields using $_FILE[] but if it manages to put my database in this case only the input name that is type text (because for the text type I use $_POST[] ).

Why is this happening? Is there another option to upload an image to a database through a form in Wordpress?