Now, even without reading the strip, I can tell this is a satire about how technology is making us less human and being used more for reproductive choices (selective traits and such) like in Gattaca. That is not how the anti-gay marriage site was using it, though.
Zach supports marriage equality and he discovered something interesting. The image was hotlinked. In other words, whatever image was in that space on his web page is what the anti-gay marriage site would display. So he made a change....
Zach? We ever meet, I have to buy you lunch. You're my kind of fellow.
Aw, someone doesn't understand technology and it bit them in the ass.