convert MiniMagick::Image to ActionDispatch::Http::UploadedFile in rails

Question

I am using Rails api app. I have a Post model. I want to upload pictures for my Post model. I want to optimize the image before saving it.

Here is my create method of PostsController:

  def create
    image = MiniMagick::Image.open(File.open(params[:post][:pictures][0].tempfile))
    image.resize "100x100"
    params[:post][:pictures] = [image]
    post = Current.user.posts.build(post_params)
    post.pictures = [image]
    if post.save
      render_success(:created, post, meta: { message: 'Post created' })
    else
      render_error(422, post.errors, message: 'Failed to create post')
    end
  end

I am getting error Pictures attachments is invalid