Power apps have two image controls. 

1. Camera
2. Add picture

Option one, uses a device built in camera. However, the image will be of a lower quality. The reason the image data utilises URL data format.

Option two, enables you to select a picture stored on your device alternatively the devices camera. This option enables you to utilise binary data format. What this means is your app has access to your camera devices high quality options.

Option two is the most popular choice. Choosing ‘add picture’ requires Flow. The reason being Power Apps doesn’t have any methods for transforming one data format into another. Flow takes your power App image and outputs your image to SharePoint Online. 

Create Power App Image capture. 

Open Microsoft Power App click here…

Create a Canvas Power App see image below.

Choose phone layout

Select Insert>Media>Add Picture
See image below.

Next select and add a button see image below.

Re-position the button as shown in the image below.