Navigate to observation listing and click on the observation that you want to add attachments to: 

Once the observation is displayed, you can scroll down to the "Comments" section and click the attachment or image button. It will open a separate window, which allows you to add images or attachments of different format and sizes:

You can comment by clicking on the comment box:

Click "comment" button once you are done:

You can click on the "vertical ellipsis" button if you want to edit or delete the comment:

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