This is an interesting problem with true E2E solutions. The person sending you the image would need to send it with lower resolution. There is no way for the se

This is an interesting problem with true E2E solutions. The person sending you the image would need to send it with lower resolution. There is no way for the server to do it for you. The servers also don't store messages once they been delivered. There is no way to get a low resolution while mobile and getting the higher resolution while on WiFi. Signal does already have the method to disable media downloads while not on WiFi, but does not have a method to tell the sender to send lower fidelity content.