the doc says:
If the process definition’s deployment contains an image resource with the same file name as the process definition
This was an old approach before bpmn.io was available. The Modeleing tool generated a png file of the process model and deployed both, picture and xml file in the same deployment to the engine.
Today you usually deploy the xml only and use the bpmn-js viewer to render the process model in the browser.
No picture is required any more and bpmn-js viewer does the job.
You can find a simple example here: camunda-7-code-examples/snippets/jsf-simple-tasklist at main · camunda-consulting/camunda-7-code-examples · GitHub
Hope this helps, Ingo