Image must be an image

I have one problem with uploading image Validation. I uploaded valid format of image but the error said "Photo must be image."

THis is my validation.

'photos'=>'required| image',

This is my form.

<form method="post" action="{{route('new.product')}}" enctype="multipart/form-data">
                      @csrf

						<div class="col-md-9">
                                    <label for="photos"  class="col-form-label input-label">Upload Photo</label>
                                    <div class="custom-file">
                                    <input type="file" class="form-control input-label shadow @if($errors->has('photos'))is-invalid @endif" id="photos" name="photos[]" multiple value="{{old('photos')}}">
                                    @if($errors->has('photos'))<span class="invalid_feedback text-danger" style="font-size: 10px;">{{$errors->first('photos')}}</span> @endif
                                    </div>
                                </div>
</form>

Please help me to figure out this problem. Thank you in advance.