When using a file upload input on an HTML page to allow images to be uploaded,
you should use the Image constraint instead of the more generic File
one. Besides restricting the allowed mime-types, it exposes additional options
specific to images like validating the image height or their width.
And as of Symfony 2.4, you can also validate the image aspect ratio (defined as
width / height) and selectively allow square, landscape, and portrait image
orientations with the new maxRatio, minRatio, allowSquare,
allowLandscape, and allowPortrait options.
Read the Image
constraint documentation page for more information.