I want to use Material Design icons provided by Google in my web app.
According Apache License I guess I must mention the author.
How should I do it?
a) Write into footer something like: "All icons are licensed under Apache License"?
b) Write into footer "Web app includes icons from authors A,B,C,D etc. (it is so annoying...)
c) Create page, which includes list of all items under license (so it is not directly in app, but beside)
d) Must I provide link to license from every single icons?
You do not need to explicitly include the licence in the footer nor create a separate page for it. In the Material Icons Guide it says
Licensing
We have made these icons available for you to incorporate them into your products under the Apache License Version 2.0. Feel free to remix and re-share these icons and documentation in your products. We'd love attribution in your app's about screen, but it's not required. The only thing we ask is that you not re-sell the icons themselves.
You are using the icons in a web app, so there is no installer or other redistributable package, where you would be required to include a file containing the notice.
Consider that in an Android or iOS application, where the app is downloaded and installed to the device, the icons can also be used but there is no way to include a separate notice... In those cases you would likely include the notice within the source code, perhaps in the main class, so that if the package were to be decomposed then the notice would be visible.
As it says, attribution in the about screen would be appreciated but not required.
Technically, to achieve license attribution for Apache License 2.0 one must ensure that users of the software can read the full License and Notice files (i.e. the License and Notice files should be included with the deployment and be accessible, License can be in short form). In an Android app that can be as simple as dropping them into assets folder, which can be accessed by unzipping the apk or using the relatively new OSS Licenses Plugin [1]. For web, making them available in a licenses folder that is publicly accessible would suffice.
Note that your software doesn't have to be packaged or have an installer to be classed as "derivative work", any software that utilises a library/code that is licensed under Apache License 2.0 is derived from that library/code.
"Derivative Works" shall mean any work, whether in Source or Object form, that is based on (or derived from) the Work and for which the editorial revisions, annotations, elaborations, or other modifications represent, as a whole, an original work of authorship. For the purposes of this License, Derivative Works shall not include works that remain separable from, or merely link (or bind by name) to the interfaces of, the Work and Derivative Works thereof.
The clause "For the purposes of this License, Derivative Works shall not include works that remain separable from, or merely link (or bind by name) to the interfaces of, the Work and Derivative Works thereof." [2] it would seem that integrating with a SaaS library would fit that case, or in your case linking to externally hosted material icon files. The existence of Google's OSS Licenses Plugin suggests that including a library while only utilising it's interfaces still falls under "Derivative Works".
Assuming you hold the icon files on your server/in your infrastructure, your web app is effectively redistributing parts of the work.
