The lie she's referring to is the picture's title on pixiv: "あなたの事が好きです。" Or "I like your thing."

It means "I like you" (in the "love" sense).

I've started tagging this meme's pictures with uso_desu, but I'd like to know the origin of this. Anyone have better information?

Just the lyrics from Luka's Toeto :
http://www.youtube.com/watch?v=7M-cj_fCXDI

Check Clannad After Story, Ep. 20, 14:08 or so in.

Oh, I haven't seen 20 yet, that might be why.

I don't know if it's the source of the meme, but you'll be rewarded either way.

is she going to jump a shark?

shii said:

here's the translation of toeto btw

http://www.youtube.com/watch?v=LIpJXsuDJPc

Now I'm hooked on that song. Even better now that I understand the cuteness of the lyrics.