To place an image with its original dimension in inches, just click once on the page where you want the image to go, then drag it into position. InDesign will place it at the ppi specified in the image metadata, which will give it the dimensions specified in the metadata.
If you click and drag an image frame while placing the image, you are telling InDesign what size you want the image to be on the page. This will override whatever dimensions are in the image metadata with the new dimensions you have specified. In the Info panel, you will see that the "Actual PPI" and "Effective PPI" numbers are different.
If you drag out a frame and then place an image, InDesign will by default insert the image at its specified ppi, which may or may not fit in the frame, unless you've specified differently ahead of time, such as by checking "Autofit" in the control bar.
In short, you specify the image dimensions on the page, not InDesign.