Create a custom security role that literally just shows them the ServiceM8 Activity Feed by disabling High Level access to all of the sections apart from the Job Diary.
Enable the Job Diary Show Photos option.
Assign that Security Role to your marketing person.
Then share the photos you want them to use by sharing them from a job card online.
To do this, open the job, find the photos you want to share, click Actions and click Share to Feed.
(Extra Tip – sharing photos onto the activity feed via the ServiceM8 app will attach a linked job number, which would then allow them to access the job card online. You might not want them to have access to the job card and it’s actions.)