Sometimes you need QR-code to be posted somewhere to promote your Android application. You can use a lot of online tools to create such image, but from my point of view the fastest way is to use Google Chart API for this.
What do you need is to create URL-request to Google Chart API with correct parameters:

1. The main part is URL:

http://chart.apis.google.com/chart?cht=qr

where cht=qr is the first parameter saying that we need QR-code.

2. Then adding image size, for example 200×200 pixels:

http://chart.apis.google.com/chart?cht=qr&chs=200x200

3. At last you should add label to be encoded in QR-code, and you need to have direct link to Android Market with your application. To do this you need to create market:// scheme url:

market://details?id=com.your.packagename

where “com.your.packagename” is the main package name of your application. Now add it to the full charts url:

http://chart.apis.google.com/chart?cht=qr&chs=200x200&chl=market://details?id=com.yota.screentest

The result of it is the QR-code image that you can add as src to img html tag: