Tarasovych

$request->file('image');
    if ($request->hasFile('image')) {
    ...

public function show($slug)
{
    $blog     = Blog::where('slug', $slug)->firstOrFail();
    $category = Category::find($blog->category_id);

    return view('blog.show', compact('blog'));
}

Route::get('blog/{slug}', 'BlogController@show')->name('blog.show');

@foreach ($blogs as $blog)
    <a href="{{ route('blog.show', $blog->slug) }}">{{ $blog->title }}</a>
@endforeach