Where is Image field data stored

We have a custom module ProductClass, this stores information about our products and we are using this to pull information to our support site. As we want to use this data across multiple sites I have been asked to add some additional fields. One if these was a image field to store a picture of the device

I amended the api call to extract this data but the field itself just contained an ID 

I cannot find where this id then refers to get the image data, I thought it might create a record in documents but cant find any record with that ID

Can anyone help with where sugar stores images using the image field, tried googling it but all that i can find is images as note attachments