When you go to File > Place, to bring in an image into your composition, Photoshop turns it into a smart object. If you would like for the image to remain rasterized, bring up the Preferences panel by pressing Ctrl K (Mac: Command K) and under the General tab un-check “Place or Drag Raster Images as Smart Objects“.
From this point on all images that you place will no longer be converted into Smart Objects.
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