When Apple (NASDAQ:AAPL) enters your market, be concerned. The company has transformed industries like music, mobile phones and digital photography. Just look at how a phone with a decent camera has made Kodak (NYSE:EK) and others become irrelevant.

Tuesday’s announcement of the iPhone 4s was fairly underwhelming, but it included news that might make life tough for some companies.

Apple has a new app called “Cards,” which allows you to take pictures, turn them into postcards, then submit them to Apple for printing and sending. Each domestic card will cost $2.99, and foreign cards will cost $4.99.

Pretty cool. But this technology stands to put some pressure on a variety of players in the space. On Tuesday’s news, shares of American Greetings (NYSE:AM) dropped by about 6.5%, and Shutterfly’s (NASDAQ:SFLY) stock dipped by as much as 17%.

So might these companies be cannon fodder for Apple? In reality, it’s not likely. Even though the greeting card market is large, it probably is not a high priority for Apple. If anything, it is just another piece of ancillary revenue. So why not take some of it?

American Greetings and Shutterfly have the advantage of being highly focused on their core market. It means they can leverage their brand as well as their distribution footprint. In the case of Shutterfly, it has partnerships with big names like Target (NYSE:TGT), Sony (NYSE:SNE) and Adobe (NASDAQ:ADBE). Moreover, the company has a substantial user base as well as an extensive catalog of designs.

So should investors see this as an opportunity to buy Shutterfly or American Greetings on the weakness?

Probably not for American Greetings, which remains a primarily brick-and-mortar operator — thus, its growth ramp has been sluggish.

Shutterfly, however, does not have this problem. Consider that the company posted a 62% ramp in revenue during the latest quarter. Unfortunately, the valuation remains fairly robust, at 75 times earnings. As seen with other high-fliers — like OpenTable (NASDAQ:OPEN) or even Netflix (NASDAQ:NFLX) — it can be dangerous to play these kinds of stocks. So it probably is better to wait for a much more material drop in the stock price before jumping in.

Tom Taulli is the author of “All About Short Selling” and “All About Commodities.” You can also find him at Twitter account @ttaulli. He does not own a position in any of the stocks named here.