I think there is a way you can upload or send pictures from your SD card while on your 3DS. You just have to use the internet browser app on the 3DS, I believe?
I heard that the Miiverse screenshot has much higher quality, though. I took some screenshots of my town using the 3DS camera and they look awful D:Yeah I just visited this page in my 3DS browser and uploaded it that way!
theres also a way to do it through Miiverse but you can't use already existing photos unfortunately. (Miiverse takes the screenshot through the app so you can take too OR bottom screen shots and then use the url for the photo)
Yukari, thank you!!
I heard that the Miiverse screenshot has much higher quality, though. I took some screenshots of my town using the 3DS camera and they look awful D: