Creating the workflow
I will not go through how to create the workflow, but i want to point to an important point.
When you create a task for approval, you have to inset the following logic.
If task is approved > Set the Photo hidden column to the URL of the matching photo in the picture library you created previously.
This means if for example the stage one approval is completed and approved, then we will set the Photo field to the URL of the picture describing this phase.
So now after creating a request and approving the first task, we can see the workflow filling the Photo field.
Creating the Dashboard
First of all, go to the Submit Request list, and create a view that includes the columns you want to show in the dashboard. Do not select the Photo column. I prefer the Box style for the view.
Finally, it is time to create the dashboard. Simply, add a new Page and call it (Dashboard).
Go to Inset Tab and click App Part > Submit Request. Make sure to edit the web part and choose the view you previously created. Also choose (No Toolbar) for the toolbar type.
Now add another App Part in the page, which is Image Viewer under Media and Content.
You can use Query String URL filter and data connections to send data between the two web parts so that the Image Viewer web part will read the photo URL from the Submit Request Photo column.