How to return image blob (base64) and strings together from Controller to frontend?

I have an AJAX call that needs to get both array of data (strings) and an image base64 blob:

// From Controller
$data = [];
$details = Model::find($id);
$image = ModelImage::find($image_id);

$data['details'] = $details;
$data['image'] = $image;

return $data;

But I get the following error:

Malformed UTF-8 characters, possibly incorrectly encoded

So I even tried to do:

$data['image'] = mb_convert_encoding($image, 'UTF-8', 'UTF-8');

But then the error becomes:

Method Illuminate\Database\Eloquent\Collection::__toString() must return a string value

How can I return both values (details and blob) from controller then?

Thanks