Figures sit straight on the white page. No frame, no rule, no shadow: the system defines none of those. Prefer a transparent PNG. Four widths ship, 5.2in, 5.6in, 6.3in, and 7.0in; pick the one that keeps the source image above roughly 190dpi at print scale, and never upscale past native pixels or re-encode the source. The four width samples run one landscape asset at all four sizes on purpose: a portrait stand-in sizes by width and grows tall, so the four widths read as four heights instead.
Screenshots only. A UI screenshot is white to its own edge and has no edge of its own, so it takes a 0.5pt hairline. An illustration, a render, a map, a chart, or a transparent PNG does not. The width and height custom properties are set inline from the source image, both or neither; the shot above is 1440 by 900 at 6.3in by 3.94in, which prints at about 228dpi.
Four widths, the figure row, and the screenshot exception. Captions 10.5pt quiet ink, centred, 6pt under the image. The seat map is 1104 by 745, so it holds above 190dpi through 5.6in and is shown at the wider two to compare the widths.