Making art for artboard

The images are placing into Illustrator over-sized because they probably have a screen-based resolution setting of something like 72ppi yet have fairly big pixel counts. An image with 1920 X 1080 pixels and a 72ppi resolution setting will place into an Illustrator print document at 26.66" X 15" in size. The same 1920 X 1080 image with a 300ppi setting will place into the same Illustrator document at 6.4" X 3.6".

There isn't really any options to make images, like JPEG and PNG files, scale to fit the artboard automatically when they are placed. Depending on your workspace settings when an image is placed into an Illustrator document it remains selected and the property bar may show the image's physical size. If I need to re-size the image I'll just type the desired numbers into the X or Y value.