I suggest that you first get permission to photograph the lichen if the property is not yours. You should examine the lichen carefully as well as photograph it. You could then look at a suitable book about lichens to identify the specimen and learn about its status in your country. You could contact a local scientist who studies lichens if a book doesn't help you. A local conservation or nature organization might also be able to help you.
Based on what I have read recently, other chemicals with antibiotic properties have been found in certain lichens. The chemicals have been weak antibiotics, however, so they probably won't be helpful for us.