The problem: upload photos to Picasa (trivial); 2) scale them if neccessary before upload; 3) if photos contains some EXIF tags (geotags in particular) copy these tags to Picasa as well.

To achieve the above I use: googleCL (upload), convert (from ImageMagick bundle for scaling) exiftool (for metadata extraction/manipulation).

Using convert the script below (jpgresize.sh) scale picture to 2048 pixels along longest side:

#!/bin/bash
# Scale pictures to 2048 pixels along longest side for upload to Picasa
# Photos below 2048 x 2048 pixels do not count towards storage limit
# (cf. https://support.google.com/picasa/answer/6558?hl=en )
#
PICASA_FREE_LIMIT=2048

while test $# -gt 0; do
  case "$1" in
    -o)  shift; OUT_FILE="$1";;
   -o*)  OUT_FILE="`echo :$1 | sed 's/^:-o//'`";;
     *)  FILE="$1";;
  esac
  shift
done

if [ -z "$OUT_FILE" ] ; then
    my_pic="${FILE%.*}_s.${FILE#*.}"
else
    my_pic="$OUT_FILE";
fi 

if [ -f "$FILE" ] ; then

  echo "** converting $FILE to $my_pic ***"

  SIZE="2048x"

  my_pic_width=`exiftool -ImageWidth "$FILE" | awk '{print $NF}'`
  my_pic_height=`exiftool -ImageHeight "$FILE" | awk '{print $NF}'`

  if [[ ( -z "$my_pic_width" ) || ( -z "$my_pic_height" ) ]] ; then 
       echo "*** $FILE has 0 width and/or height ***"; exit ;
  fi

  ## http://www.imagemagick.org/Usage/resize/#resize
  if [[ ( "$my_pic_width" -gt "$PICASA_FREE_LIMIT" ) || \
      ( "$my_pic_height" -gt "$PICASA_FREE_LIMIT" ) ]] ; then
      if [ "$my_pic_width" -gt "$my_pic_height" ] ; then
        SIZE="${PICASA_FREE_LIMIT}x>"
	echo "*** $FILE width: $my_pic_width ; converting to $SIZE"
	convert "$FILE" -geometry $SIZE "$my_pic"
      else
        SIZE="x$PICASA_FREE_LIMIT>"
	echo "*** $FILE height: $my_pic_height ; converting to $SIZE"
	convert "$FILE" -geometry $SIZE "$my_pic"
      fi
   else
      ## File is too small copy the original:
      echo "*** $FILE has $my_pic_width in width; COPYING"
      cp "$FILE" "$my_pic"
   fi
else 
   echo "*** FILE $FILE not found! ***"
fi

Upload one picture to picasa with 1photo2picasa.sh

#!/bin/bash
#
# Upload photo to Picasa with googleCL
# It is assumed the photo contains UserComment GPSLatitude GPSLongitude GPSAltitude 
# Exif tags which are copied to Picasa (see below for more details)
# 
# Default album title:
ALBUMTITLE="???" 

echo "$0 -a AlbumTitle FILE-2-UPLOAD"

while test $# -gt 0; do
  case "$1" in
    -a)  shift; ALBUMTITLE="$1";;
   -a*)  ALBUMTITLE="`echo :$1 | sed 's/^:-a//'`";;
     *)  FILE="$1";;
  esac
  shift
done

AUTHOR=`exiftool -S -Artist $FILE`

if [ -z  "$AUTHOR" ] ; then 
   # It there is no Artist tag it is assumed photo was not tagged properly
   echo "*** ERROR: $FILE lacks Artist EXIF tag"
   exit;
else  
   ## Some tags are edited:
   TAGS=`exiftool -S -UserComment $FILE | awk '{ $1=""; for (i=1;i<=NF;i++) { if ($i ~ /http/) { $i=""}}; \
    gsub (/, +/, ",", $0); gsub (/ +,/, ",", $0);  gsub (/^ +| +$/, "", $0); print $0}'`
   GPSLat=`exiftool -S -c '%+.6f' -GPSLatitude $FILE | awk '{ print $2}'`
   GPSLon=`exiftool -S -c '%+.6f' -GPSLongitude $FILE | awk '{ print $2}'`
   GPSAlt=`exiftool -GPSAltitude $FILE -S -c "%.1f" | awk '{ if ($0 ~ /Below/) { print -$2} else {print $2}}'`

   PICASA_TAGS=""
   ## Concatenate all tags
   if [ -n  "$TAGS" ]   ; then  PICASA_TAGS="$TAGS";  fi
   if [ -n  "$GPSLat" ] ; then  PICASA_TAGS="$PICASA_TAGS,geo:lat=$GPSLat"; fi
   if [ -n  "$GPSLon" ] ; then  PICASA_TAGS="$PICASA_TAGS,geo:lon=$GPSLon"; fi
   if [ -n  "$GPSAlt" ] ; then  PICASA_TAGS="$PICASA_TAGS,geo:alt=$GPSAlt"; fi

   #  Upload to picasa:
   google picasa post --title "$ALBUMTITLE" --src="$FILE" --photo="$FILE" --tags="$PICASA_TAGS"
fi

Finally simple bash script upload2picassa.sh uses jpgresize.sh and 1photo2picasa.sh to upload all .jpg files from the current directory to picasa:

#!/bin/bash
# Upload all .jpg files (scaled tp 2048) to picasa 
#
echo "Uploading all .jpg files to album: $albumtitle"

albumtitle=$1

if [ -z "$albumtitle" ] ; then
  echo "Podaj ID albumu!";  exit 1
fi

for file in *.jpg; do

  echo "Uploading $file to $albumtitle album..."

  outfile="${file%.*}_s.${file#*.}"

  jpgresize.sh -p  -o $outfile $file  && 1photo2picasa.sh  -a $albumtitle $outfile
done