drag the picture over the clips in your timeline
resize it by using the Transformation settings, position it
=> you get a tiny rectangle with your logo
if your logo is NOT an rectangle, the graphic file has to contain alpha-info = transparency; jpg is a codec which doesn't transport alphas ...
example:
- on left, a logo, jpg, rectangle
- open it in Preview,app (pre-installed on any Mac)
- click on Selection, choose the Magic Wand for transparencies
- click into the white 'background' and drag the mouse to in-/decrease threshold
- release mouse, background selected
- hit the back key = erase selection
- save new version as png, check alpha
dragging THIS png-version onto the clips in your timeline keeps the individual form, use the transform settings to make it smaller and positioning it ...