Why a List? I think you may find that dictionaries when serialized to json, at least using the DataContractJsonSerializer (fyi available with the 3.5 framework only, with the 2.0 or 3.0 framework you'd need to bolt on aspnet ajax and use is json serializer), are a little more cumbersome to work with than how a list would serialize. Although that is subjective.
There are implications too with your client side code. Now on the client side you'll have an array of the json serialized MyImageResourceClass instances. You'd need to iterate through this array creating your "img" tags as you go.
Hopefully these ideas and suggestions can help get you going! And no doubt there are other solutions. I'm interested to see what comes of this.