Quote Is there a way to import an image at its actual size, rather than having it fill the frame automatically? If not, is there a way to batch-select all the images at once and resize them the same?

Yes. PD assumes that every image you put on the timeline should be rescaled to fit the whole screen, which is usually the right call because image pixel sizes can vary so widely.

For your quest, simply size and place the first image exactly where you want it to appear on the screen, then right click and choose Copy Keyframe Attributes. Now place all of your other diagrams on the timeline, drag the selection rectangle around ("lasso") them, then right click on any one and choose Paste Keyframe Attributes. Voila, all the selected clips are formatted exactly the same

PD actually has two different clipboards, the main one that's used for content and can accept content from Windows, and a separate one for keyframe attributes. That means that you can do all kinds of normal editing and still paste the same keyframe attributes to other clips later on, as long as you don't close PD.

Perfect! Many thanks for the prompt reply.