Rails customize json generating using eagerloading rails

I have a model User and another Images and relationship in between both of these as:

User has_many :images

Image belongs_to :user

Now I'm writing a json api to get user with his images using eagerloading like,

User.all.as_json({:include=> {:images => {only: [:image_url] } })

Now I want to get images and want to override JSON at the time of generating like we can override as_json method in my user model same as I want to override at time time of include, but that is not generating using as_json in Image Model.