for anyone that comes across this thread and is also confused - wherever you want to display the image, you’ll have to interpolate the base url (which was mentioned in a previous comment) with the rest of the image path that you got on your response.
at time of writing this, the baseURL is indeed https://img.opencritic.com/

Happy coding!

Images work for me. If you check eg. https://opencritic.com/game/3717/red-dead-redemption-2 you see that the img base url is

https://img.opencritic.com/

Were you eventually able to use images?