<div class="input-group">
          <div class="input-group-prepend">
            <span class="input-group-text" id="inputGroupFileAddon01">Imagen</span>
          </div>
          <div class="custom-file">

            <input type="file" class="custom-file-input" id="imagen"  name="imagen"   capture="camera" accept="image/*">

            <label id="casillaFileName" class="custom-file-label" >Examinar...</label>
          </div>
        </div>

$('.custom-file-input').on('change', function(event) {
            var inputFile = event.currentTarget;
            $(inputFile).parent()
                .find('.custom-file-label')
                .html(inputFile.files[0].name);
        });