Hi Eduard, welcome to Community and congrats on your first post. The Wolfram|Alpha App provides convenient mobile access to Wolfram|Alpha along with limited step by step functionality. Image input is also possible through an in-app purchase on iOS.
Wolfram|Alpha Pro is a subscription which provides a host of features on the web. Just a few of the features are: complete access to Step-by-step solutions, the Wolfram Problem Generator, dynamic interactivity, additional input options, ability to customize and download results, and more!
Coming soon, Pro subscribers will be able to unlock additional features within the Wolfram|Alpha iOS App. Also, Pro subscribers will soon see some really neat new features on the web . . .