The script: 1) suspend capturing images at night for obvious reason and 2) writes images to files named as: image_<odd-or-even-week><day-of-week>_<hour><minute>.jpg

Thus only images from the last two weeks are stored and the older ones are deleted ``automatically''.

#!/bin/bash
OUTPUT_DIR=/var/www/cam/fswebcam-output
# Max resolution for C270 webcam is 1280x720
RESOLUTION="1280x720"
QUALITY="85"

MINUTE=`date +%M`
HOUR=`date +%H`
MONTH=`date +%m`
DAY_OF_WEEK=`date +%u`
WEEK=`date +%U`
FILE_OUT=`date +%d%H%M`
TODAY=`date +%Y/%m/%d`

## Suspend capturing pictures at night
DAY_START=`sun_calc.py -date "$TODAY" -city Sopot -param dawn`
DAY_STOP=`sun_calc.py -date "$TODAY" -city Sopot -param dusk`

if [ "$DAY_START" = "False" -o "$DAY_STOP" = "True" ] ; then
     NIGHT="YES"; exit;
fi

fswebcam -r $RESOLUTION -S 11 --jpeg $QUALITY \
   --title "Sopot/Abrahama Street (PL)" \
   --subtitle "View from my window" \
   --info "Logitech_Webcam_C270@raspberryPi ($RESOLUTION)" \
   --save $OUTPUT_DIR/image.jpg -q

## Rotate photos every two weeks
## Week number modulo 2 (0 or 1)
WEEK_NO=$(($WEEK % 2))
FILE_OUT="${WEEK_NO}${DAY_OF_WEEK}_$HOUR$MINUTE"

## Wundergound expects the file is `image.jpg'.
## To preserve from overwriting rename:
cd $OUTPUT_DIR && cp image.jpg image_$FILE_OUT.jpg

./sun_calc.py is a Python script (I am not Python programmer BTW):

#!/usr/bin/python
import datetime
import argparse
import pytz
from astral import Astral
city_name = 'Sopot'

parser = argparse.ArgumentParser()
parser.add_argument("-date", type=str, help="Date as yyyy/mm/dd")
parser.add_argument("-city", type=str, help="City name")
parser.add_argument("-param", type=str, help="dusk sunrise sunset or dawn")
parser.add_argument("-verbose", help="Icrease verbosity", action="store_true")
args = parser.parse_args()

dat = args.date
city_name = args.city
param = args.param
verb_level = args.verbose

[year, month, day] = dat.split("/");

year = int(year)
month = int(month)
day = int(day)

a = Astral()
city = a[city_name]

a.solar_depression = 6 ## sd can be:  6, 12, 18

timezone = city.timezone

sun = city.sun(date=datetime.date(year, month, day), local=False)
sun_local = city.sun(date=datetime.date(year, month, day), local=True)

time_now = datetime.datetime.utcnow().replace(tzinfo = pytz.utc)

if verb_level > 0:
        print('solar_depressions: ' + str(a.solar_depression))

        print city_name + " " + str(time_now) + " " + str(sun[param]) \
	        + " (" + str(sun_local[param]) + ")"

print time_now > sun[param]

The script based on astral package can compute dusk/dawn time (among other things) and compares it to the current time. If current time is past dusk/dawn (specified as a command line parameter) ./sun_calc.py returns True. Otherwise it returns False.

The astral package does not contains Sopot but it is easy to add it just by editing astral.py (before installation of course):

Sopot,Poland,54°44'N,18°55'E,Europe/Warsaw

A short test demonstrating that for Sopot and Warsow the script returns significantly different results:

./sun_calc.py -date 2013/01/21 -city Sopot -param dawn -verbose
solar_depressions: 6.0
Sopot 2013-01-21 09:17:11.368979+00:00 2013-01-21 06:09:47+00:00 (2013-01-21 07:09:47+01:00)
./sun_calc.py -date 2013/01/21 -city Warsaw -param dawn -verbose
solar_depressions: 6.0
Warsaw 2013-01-21 09:17:46.172157+00:00 2013-01-21 05:53:22+00:00 (2013-01-21 06:53:22+01:00)
True

So there is circa 15 minutes difference between Sopot which is some 300 km to the North from Warsaw.