draw on a picturebox image

As nobrainer said, you may want to try mouse_down event and store positions in an array and when done, draw the path. You can save this array in some persistent form, so when you load your picture again, it will read positions of the path from the persistent storage and draw the path again. If you want to add the path into the image permanently, you need to create a Graphics object from the Bitmap, draw the image, draw the path, and save the Bitmap object. See GDI+ section of C# Corner. I wrote one article on how to insert graphics objects to an image.

Drawing marks or paths on the image isn't just putting a pixel at the mouseposition when the mouse moves. When using this method and you move the mouse fast there will be holes in the path. So maybe (when the mouse is down) you can record some anchor points and draw the final path when the mouse is released from those anchor points. I hope this idea is somehow helpfull :)

Hello, I'm working on a project of pathfinding ... I have an image map (in a picture box) and the user have the possibility to put points and paths on the image ... And for helping the user I have put a system of marks (like Photoshop for example). So I load the image map, I draw the points and the paths (from database) on the image map, but I have problem with drawing my marks in the MouseMove I don't know if my explanations are quite precise ... Thanks a lot

You have to be more specific. It all depends on your equiement and how frequent you wan to redraw the image.