If all of the images have the same extension the following command (when run in Terminal.app) will search your directory for files with that specific extension and open them in Preview.
find /yourdir -maxdepth 1 -type f -name '*.jpg' -exec open -a /Applications/Preview.app {} \;
If you want to search through multiple directories and not stop at the root directory (in this case "yourdir" you can remove the "-maxdepth 1" portion.
If you want to search for multiple file extensions (jpg and tif) use the following command.
find /yourdir -maxdepth 1 -type f \( -name '*.jpg' -o -name '*.tif' \) -exec open -a /Applications/Preview.app {} \;