Инсталиране на Intervention\Image:

composer require intervention/image

В Laravel > 5.4 автоматично се регистрират пакетите.
Функция за ъплоуд на изображения - с проверка и преоразмеряване ако снимката е над 1200 пиксела по ширина или височина със запазване на съотношението на изображението:

 <?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use Illuminate\Support\Facades\Storage;
use Image;

class ImageUploadController extends Controller
{

    protected $file;
    protected $filename_to_store;
    protected $dir_to_store;
    protected $image_path;
    protected $image_width = 1200;
    protected $image_height = 1200;

    public function storeImage(Request $request)
    {
        request()->validate(['image' => ['required', 'image', 'mimes:jpeg,png,jpg,gif,svg']]);

        $this->getPaths($request->file('image'));

        $this->uploadImage();

        return response(asset('storage/'.$this->image_path), 200);
    }
    public function storeIcon(Request $request)
    {
        request()->validate(['icon' => ['required', 'image', 'mimes:jpeg,png,jpg,gif,svg']]);
        $this->getPaths($request->file('icon'), 'icons');
        $this->image_width = 120;
        $this->image_height = 120;
        $this->uploadImage();

        return response(asset('storage/'.$this->image_path), 200);
    }

    private function getPaths($file, $type = 'images')
    {
        $this->file = $file;
        $this->dir_to_store = $type . '/' . date('Y/m/d/');
        Storage::makeDirectory('public/' . $this->dir_to_store);

        $filename = pathinfo($this->file->getClientOriginalName(), PATHINFO_FILENAME);
        $this->filename_to_store = $filename . '_' . time() . '.' . $this->file->getClientOriginalExtension();
        $this->image_path = $this->dir_to_store . $this->filename_to_store;
    }

    private function uploadImage()
    {
        $img = Image::make($this->file);
        $img->height() > $img->width() ? $this->image_width=null : $this->image_height=null;
        $img->resize($this->image_width, $this->image_height, function ($constraint) {
            $constraint->aspectRatio();
        })
            ->save('storage/'. $this->image_path);
    }
}