Search engines cannot "see" pictures, they read text. You can help the search engines "see" the topic of your pictures by giving them something called an "alternate attribute" or "alternate text".
If you added the picture using the Picture Widget, you can add alt text as follows:
1. Click on the Picture Widget in your page, and then click "Edit" in the top left corner.
2. Under "Alternative Text", enter your description in the box provided.
3. When you have typed in your text, click Save.