A
SignalR application might be the simplest way to do this, see this example:
CodePlex Archive[
^] but there is a limit to the size of the pictures that can be sent.
The CodePlex example uses
IIS, but it is also possible to make an even simpler
selfhosted SignalR application, see:
Tutorial: SignalR Self-Host | Microsoft Docs[
^]
Here is another interesting SignalR chat app with pictures:
[
Chat app]
If you have to send larger pictures,
TCP would be a better choice, see:
TcpClient Class (System.Net.Sockets)[
^]
You could also use a simple web server like "USB webserver on a stick", XAMPP or something similar to handle the bulk of the file tranfers and use SignalR for the communication.
Just place the files in the root directory of the web server, then you can use e.g. htttp://1.2.3.4/myfile.jpg to download it with
WebClient.DownloadFile().
See:
WebClient.DownloadFile Method (String, String) (System.Net)[
^]