When I render an image, the render uses the camera perspective. What setting do I need to change to have the render show the user perspective?
There is no real way to do that. (For example many settings like defocus depend on the camera object.) You simply will have to move the camera around.
Firstly: You can move the camera around like any object (grab with G, rotate with R and scale with S), but it is easier to go to the camera perspective (numpad 0) and enter fly mode (Shift+F). This allows you to position the camera in a more practical way. (See this in more detail here: https://youtu.be/xcZmyD9jkI4)
Secondly: If you want to save the camera's position for some reason, you can simply add a new one to the scene (Shift+A) and set it to be the active camera by pressing the Ctrl + 0 hotkey. Now the scene will be rendered from it and hitting 0 will make you look through it. You can tell which camera is active by looking at the camera object from another view: the small triangle above it is filled when it's active.
Thirdly: If your user perspective is "just the right way", you can align the camera to it (I can't remember the hotkey, but hitting space and looking for something along the lines of "Align camera to view" should get it).
this can be achieved only for 3D view port. Here you have to go:
So the result will be the object+outline[unselected, selected, active] color without grid and axis lines.
keep in mind that the size of the render will be rounded on width and height present in the properties window under render tab, or with shift+z you can render the final scene with the user perspective, but with a complex scene this can be a pain for your cpu
You cannot actually render from the user perspective (excluding OpenGL viewport quality renders). Instead, you can simple move the camera to the user perspective using CtrlAlt0. If you want the camera to stay locked to the view, there is an option to do that in the properties panel (accessed by hitting N):
You can easily switch between Perspective and Orthographic rendering, not just the viewport as other answers may suggest.