You say you'll change the resolution . . .

"You say you got a real solution, well, you know . . . we'd all love to see the plan (the Beatles, Revolution)." If you remember from last week, the web was actually around in the 60's, so maybe John Lenon was on to something when he wrote this song and maybe, he meant resolution!
See, the story goes that Ringo was actually trying to send John a picture of Chairman Mao over the Internet. Unfortunately, John was tired of waiting for the picture to load and the rest is history, thus the song!
This was a bad idea to just attach and send the picture. If Ringo would have taken the time to do a little homework, he would have understood a few basic concepts when dealing with digital photography (just play along).
The original picture of Chairman Mao was originally printed using CMYK color. When the actual digital picture was uploaded, index color was used. Though the pic might looked dithered, RGB colors would now be used on the computer image (yes, all 256 colors).
There are several different forms of file formatting that Ringo could have used in this situation (TIFF, JPEG, GIF, etc.) The file format tells the computer what kind of file it is. Typically with a picture, Ringo should have saved the image as a JPEG. A JPEG file can contain 16.7 million colors also known as 24 bit which is preferred for digital photographs.
Ringo could have also compressed the file. There are several ways to compress a file. Cropping the picture by cutting out all the unnecessary "white space" changes the amount of pixels being sent. Since Ringo probably didn't know any better, 800 x 600 pixels is a safe way to send the picture using 72 ppi. He could have re-sized the picture which would have changed the size of the picture without affecting quality. He could have also sent the picture using a medium quality versus a higher quality resolution.
To ensure better speed when opening the photo, Ringo should have checked the KB of the photo. It is good to keep the image between 30 & 100KB. He could have also used a feature called re-sampling but this changes the pixel dimensions and negatively affects the quality of the picture.
After all of this, you ask, why didn't he just scan the original printed photo instead of uploading the digital photograph. Great question! See, a scanner analyzes an image by use of OCR (optical character recognition). So in this case, Ringo's scanner did not have the best optical resolution so interpolation could have occurred which would have derogated the quality of the photo.
Lenon finished his song, "But if you go carrying pictures of chairman Mao, you ain't going to make it with anyone anyhow. Don't you know it's gonna be all right." John wrote this song for Ringo explaining the importance of resolution and it was all right, all right, all right!