All image layers are rasterized and rendered as shown in your PSD.

In reality, an image is an image! You dont save much by applying a dropshadow to an image at runtime vs. loading a PNG.

Image Layers with Effects

Layer becomes rasterized/flattened

All layer effects and styles are rasterized and rendered with the image in the Output.

External Images

No change, rendered as is

Any image file you open in your PSD (jpg, png, or gif) will render as is in the Output.

Rasterized Images

No change, rendered as is

Any layer [rasterized] in your PSD will render as is in the Output.