Using Visual Studio, it is really easy to work with webservices.
Create a new webservice project.
Here you create two methods: voi UploadImage(byte data, string filePath) and byte DownloadImage(string filePath)
The create your Client.
To use your webservice right-click on references -> Add Service Reference
Now you can add your service and give it a name.
Now you can initialize a webservice-object. With this you can access your methods.
Have a look at a tutorial like this one
. There are many out in the web.
It is really easy to learn and use.
Hope I could help.