Migrating images and files
Thank you for Berdir's help but I noticed that I was missing some information on my drupal7_fruit migration file like the values for field_image and migration dependencies.

The working solution:

migrate_plus.migration.drupal7_image.yml

id: drupal7_image
label: Images
migration_group: drupal7
migration_tags:
  - Drupal 7
source:
  plugin: d7_file
  constants:
    source_base_path: '/var/www/username/drupal7/' # Full location of your drupal7 site
process:
  fid: fid
  filename: filename
  source_full_path:
    -
      plugin: concat
      delimiter: /
      source:
        - constants/source_base_path
        - filepath
    -
      plugin: urlencode
  uri:
    plugin: file_copy
    source:
      - '@source_full_path'
      - uri
  filemime: filemime
  status: status
  created: timestamp
  changed: timestamp
  uid: uid
destination:
  plugin: entity:file
migration_dependencies: {}


migration_plus.migration.drupal7_fruit.yml

id: drupal7_fruta
label: "Migrate Fruit Content Type"
migration_group: drupal7
migration_tags:
  - Drupal 7
source:
  plugin: d7_node
  node_type: fruit
process:
  nid: nid
  vid: vid
  langcode:
    plugin: default_value
    source: language
    default_value: und
  title: title
  uid: node_uid
  status: status
  created: created
  changed: changed
  promote: promote
  sticky: sticky
  revision_uid: revision_uid
  revision_log: log
  revision_timestamp: timestamp
  field_description: field_body
  field_image: # Image field name in Drupal 8 site
    plugin: iterator
    source: field_photo # Image field name in Drupal 7 site
    process:
      target_id: fid
      alt: alt
      title: title
      width: width
      height: height
destination:
  plugin: 'entity:node'
  default_bundle: fruit    

migration_dependencies:
  required: 
    - drupal7_image


Hope this may help anyone with the same problem in the future!