Possibly but what matters is units. Doesn't make much difference if they're mm, meters, inches or miles, so long as the drawing is done in a know unit it's easy to convert to the correct scale. You may be able to do an accurate drawing from an image but personally I wouldn't even attempt it, too many things like fisheye on the lens and not being perfectly square that could effect it. An image in the background might sometimes help with positioning and clearance cuttouts but not good practice to use them for accurate dimensions.
A few things that may help with LibreCAD:
Snap to grid. It changes resolution as you zoom so it's as easy to place something to the cm as the micron.
Line types. Tangent, orthogonal, parallel through point and parallel at a distance save loads of time.
Modify: Move, rotate, mirror etc, makes repetitive drawing much easier.
Attaching a simple sketch with ordered layers for a torque-armish thing to show how my workflow typically goes:
0, centre lines, in this case the axle slot and lower tube in-line and upper tube at 45 degrees.
1, parallel lines at the distances required, a 16mm slot and 4 u-blots with 24mm centres to clamp onto the frame tubes.
2. hole centres along those lines, first a couple of orthogonal lines at the centre point and then 2 more on each at 40mm and 60mm for the u-bolts and one at 25mm for the rear of the axle slot.
3. holes, 8x 6.2mm (3.1 radius) for the u-bolts and one at 28 for the axle.
4. the slot can be drawn at this stage, just lines between points for the top and bottom and a curve with the centre, distance and start and finish points. Curves and angles are done anti-clockwise, counter-intuitive but you get used to it :/ Layers 0, 1 and 2 can be hidden or deleted at this stage, they've done everything they need to do.
5. Rough out for an outline at least 5mm away from everything, parallel at a distance will also do circles so just 2 lines 5mm away from the axle slot lines and the relevant u-bolt holes.
6. 2 point to point lines from the end of the slot to the lines just drawn at 5mm distance, 2 point to tangent lines from the end of those to the circles around the u-bolt holes, 4 tangent to tangent lines between the circles around the u-bolt holes and 5 centre/distance/start/end curves to join them up. It sometimes helps to select the lines before drawing the curves so their end points are highlighted, often causes errors when also using snap to grid and they can be a pain in the ass to find.
7. Layer 5 can now be hidden, the whole lot selected with a bounding box, the axle circle de-selected with a click and modify>move used to copy and paste the selection to another layer (with the "use current layer" tickbox checked). Usually I'd do all of that on just one layer and delete as I go but it's worth getting used to using layers as they come in very useful.
Hope that makes some sense, it gets much easier with practice and most of the 3d stuff I do uses 2d from librecad imported to openscad and extruded, some fairly complex models can be built up just using different layers extruded to different heights. An openscad file is included to demonstrate, they'll need to be in the same directory and the .txt extension deleted (can't attach .scad files).
