You can use this widget to accomplish what you are trying to do
To accomplish this, you would have to create an entity in your domain model that will hold the url of the image that you just received. Then in your microflow thats calling the rest service, create this object and set the url attribute to the url you just received. Then you can pass this object to a page where you have the image viewer widget configured.
Here is an example I made in a test project. Set the image attribute field to the attribute that you are using to store the url from the rest service.
Here is an example of what your microflow can look like. Just add the create and show page activity after the rest service call in the microflow you currently have. Also replace the show message activity with the show page activity.
I just noticed there are two image viewer widgets in the app store. Try this one
I think the original one I posted was built for Mendix 5