First: You should be placing your images as links. Don’t embed and don’t copy and paste. Second: Linked images will not lose resolution, but… Third: When an image is placed as a link a low-resolution preview is generated and embedded in the Indesign file. This preview is a rendering of the image at actual size, but at 72 pixels per inch. If the source image has a lower resolution that 72 ppi then that resolution is used. For example, say you have an image that is 600 × 600 pixels with a resolution of 300 pixels per inch. Importing this image at 100% will give you a 2 inch × 2 inch image that will print at 300 pixels per inch. InDesign will generate a preview that is 144 pixels × 144 pixels. When you are using quick view this is what InDesign will show you. When you zoom in you won’t see the full resolution of the image. If that same image was 72 pixels per inch (but the same 600 × 600 pixels) and it was placed at 100% it would appear to be 8.33 inches × 8.33 inches. InDesign will generate a preview that is 600 pixels × 600 pixels. If you scale it to 24% you will get the same image as above, except zooming in will show you a higher resolution preview because a higher resolution preview is embedded in the InDesign file. This will also make your Indesign file larger since the preview is 317% larger. If you have a lot of images like this this will add up. Images downloaded from a website, stock images, and images imported from a camera often have their resolution set to 72 ppi. Some have no resolution data, since it is not a requirement for many image formats. In that case InDesign and most other programs will assume the image is 72 pixels per inch. This is why it is a good idea to prepare images at an appropriate resolution any place them at the size they need to be, rather than scaling down images that are a lower resolution. In Phoshop set the image resolution to 300 ppi in Image > Image Size (turn off resampling).
... View more