We can able to fetch the Custom Image Type product attribute value from the Product object by just fetching the product object.
Let’s say you have created a custom image_type product attribute called, brand_logo and you want to fetch the value saved for a product by product object. You can refer to the below logic to fetch the image value.
You can fetch the value of the image attribute by calling the below line,
I hope you have fetched the Product Object by the ProductRepositoryInterface, You can check the logic, Fetch Product Object By SKU
Using the above stuff, You will get the file path of the image in the response.