There doesn't seem to be a standard way to credit the author, so I would say that it depend on the author. As a general rule, though, you must include them in the credits (in a way that it's clear that you are using their images, but they don't endorse your app).
I don't think just including the notice in the source code would be enough. At the least, there should be a readme included with the app (when you give it to your customers) with the credits that come with each icon set. Another option would be adding a "credits" link at the bottom of the web app, that includes you and mentions them as the authors of the icons (and has links to their sites).
Or you can pay 50$ and forget about all this :P
@Chris I hate IE6 so much at the moment, that I have decided that as long as it just looks slightly uglier but doesn't break anything, I don't care. Of course, if the customer *cares* I would fix it, but it still has not happened.
There doesn't seem to be a standard way to credit the author, so I would say that it depend on the author. As a general rule, though, you must include them in the credits (in a way that it's clear that you are using their images, but they don't endorse your app).
I don't think just including the notice in the source code would be enough. At the least, there should be a readme included with the app (when you give it to your customers) with the credits that come with each icon set. Another option would be adding a "credits" link at the bottom of the web app, that includes you and mentions them as the authors of the icons (and has links to their sites).
Or you can pay 50$ and forget about all this :P
@Chris I hate IE6 so much at the moment, that I have decided that as long as it just looks slightly uglier but doesn't break anything, I don't care. Of course, if the customer *cares* I would fix it, but it still has not happened.