Background removal from reference image

[snibgo]

Command interpreters (bash, Windows etc) break commands at spaces, except where the space is within a quoted string. So one version of your command has quotes.

Personally, I don't have spaces in filenames. This saves some grief.

[classic12]

Sorry corrected the last one replace space with "-"
for oldname in *
do
newname=`echo $oldname | sed -e 's/ //g'`
mv "$oldname" "$newname"
done

[ptamanekar]

Use double quotes for file names