🚀 go-pugleaf

Under OSX you can use something called "image capture scripting" apparently - search in this forum for "Resolution", other people have tried and discussed the same thing.

Alternatively you should be able to write a script that will use Photoshop 7's scripting to determine resolution of images - maybe store the info in the file's comments box and retrieve that from within ID.

Otherwise... If you know that all your images will be 300dpi then you can use the absolute horizontal/vertical scale properties of image elements to ensure that they are placed at 100% size - but it doesn't look to me like ID can retrieve an image's resolution (not a property of image element).

If the images are uncompressed you might be able to infer the image size in pixels from the file size - but you'll have to account for header size unless using RAW format, and you'll still have to compute the aspect ratio from the image dimensions at 100% / 100% scale.