Ok, i'll try to explain little bit more.
On PC side is my "Fuze Import" application developped in C++ Builder that you could see in my previous video. I'have added new functionality into this application that can send whatever file (not necessary image, but really any file you want) via USB/COM port to the tiny A-Con device. This PC application simply sends a lot of commands to the A-Con that request setting buttons and analog sticks to the position that corresponds to the 4Bytes that PC application wants to transmit. For example: If i want to transmit Byte 01011101 then PC application sends command to the A-Con to press 5 buttons: A, B, L, R, ZL. For other 3 bytes it sends commands to A-Con to emulate setting JoyCon analog sticks to some specific position that again correspond to these Bytes.
On Nintendo size is my Fuze program that is still checking controler status "c = controls(0)". When it detects that some specific combination of buttons are pressed it knows that it is communicating with PC and translate this combination of actually pressed buttons and position of analofg sticks into 4Bytes.
The rest is just the communication protocol. The header block that has 32 bytes where i transmit file size of the transmitted file and its name. And then follow directly binary data of the transmitted file.
When the Fuze program receives valid header block from PC it creates a new record in the internal file and starts to write every bytes it recieves after this new record.
The same Fuze program i used to check if the data are ok. It simply reads data back from the internal file and display them as a text (when i tested text file) or draw pixels on the screen when i tested validity of image file.
Well, maybe it sounds very complicated, but when it is working, it is super smooth, relatively quick and the most important thing is that it makes this possible.
Now, you can have your own image in your games, you can create your own sprites and animation on PC, text files or whatever and transmit it as your resource into your game project.