When using the File>Open command to open an image, the image appears to be resized smaller. How do I open the image in its original size? Also, I'm not talking about File>Place.
Your document needs to have the same PPI settings as the image being loaded in.
You can load the image into Photoshop and then change the PPI and then load it into Illustrator.
I used to have this problem a lot, I've decided on 72 ppi for editing in Illustrator as it is less strenuous on my system and I usually design things that won't be printed anyhow.