Thank you for your replies.
I cannot place markers on the photos because they appear on top of the canopy in my 3d point cloud.
I took many points with my GNSS stick on the paths without placing GCP markers (since the idea is not to use them as gcp's but to "see" where the path lies in my point cloud, 3d model, orthophoto or DEM). The precision doesn't have to be high since it's only paths in the forest. Most of the time, i had a FIX signal, because there are no leaves on the trees and the baseline was 5km. I would now like to include these points in my point cloud, not as markers or references, but as points. I figured that if I run a classification on ground points afterwards, these would be included and so all the tree canopy would be classified as "vegetation" or something else. This way, I could have a more precise DTM
I recently thought of using the function "import/points" but I have to find a way to convert a CSV file into a LAS or other point cloud format. Then, I could import these points into my point cloud.
Does this sound right?