Rails Minimagick not showing error

Question

Why is alert not showing when submiting a form? Im trying to process images with Minimagick and validate image dimensions.

Model

`def validate_minimum_image_size
  image = MiniMagick::Image.open(photo.path)
  unless image[:width] > 1300 && image[:height] > 1300
  errors.add :image, alert: "My error here"
  end
 end`

THANKS