Yes, but how many ads can you have?
or you automatically generates a ton of variation of the same ads otherwise a spammer can just keep a dictionary with the ads images and the correct answer.
Better yet, build up a list of quotes organized by the brand. How many taglines can Toyota have? So even if the quoted text is obfuscated differently each time (new font, new noise), you can teach your bot to recognize the company logo and try one of the few taglines they have.