Drupal Node Reuse Image Field
So you want to reuse file that uploaded on existing node to your new node?
You can easily use Drupal module "Filefield Sources" .
After install and activate the module, you have to setting on specific image field in Content Type.
For example, choose Structure > Content Types > manage fields (on Article) > choose edit on field_image > expand File Sources then you can set which model do you want to use on Image field.
As shown on the article's image, I choose Reference existing.