Add the custom filepicker field to a form

Pass the current form object and the column name:
= custom_filepicker_field(form, :profile_image)

Create an application helper:

Optionally toggle multiple

# app/helpers/application_helper.rb
  def custom_filepicker_field(form, field_name, multiple=false)
    @multiple = multiple
    @form = form
    @field_name = field_name
    render 'shared/custom_filepicker_field'
  end

Then add the custom shared view file:

Customize if necessary, but most importantly notice the custom onchange method.

# app/views/shared/_custom_filepicker_field.html.slim
= @form.filepicker_field @field_name, services: 'COMPUTER, GOOGLE_DRIVE, WEBCAM',
                                      mimetype: 'image/*', button_class: 'btn btn-primary btn-sm',
                                      button_text: 'Select file',
                                      onchange: 'filepickerOnChange(event, $(this))',
                                      multiple: @multiple

Add a global js method to process the file selection

# app/assets/javascripts/filepicker.js.coffee
window.filepickerOnChange = (event, elem) ->
  content = '<span class="filepicker-filename">' + event.fpfile.filename + '</span>'
  elem.parent().append(content)