I have made some progress in accessing still camera with gphoto2 (cf. here). The detailed description of my set-up will be disclosed within a few weeks (as I am still not sure if it is 100% success:-). In short:

I changed camera from Canon A620 to Nikon S3000.

I connected camera with active USB hub.

On every capture USB port is reset with usb_reset utility (cf here and here)

Multiple cameras

I use two Nikon S3000 compact cameras so there is a problem how to identify which is which.

$gphoto2 --auto-detect
Model                          Port                                            
----------------------------------------------------------
Nikon Coolpix S3000 (PTP mode) usb:001,022     
Nikon Coolpix S3000 (PTP mode) usb:001,021  

So one can use --port usb:001,022 option to access first attached camera and --port usb:001,021 to access the second one. Of course hard-coded port numbers are troublesome as they are not fixed and change if the device is disconnected/connected again. Better way to identify the camera is to use it's serial number:

## $gphoto2  --get-config serialnumber --port PORT
## example
$gphoto2  --get-config serialnumber --port usb:001,022
Label: Serial Number                                                           
Type: TEXT
Current: 000047514512

I have black Nikon with 000041076602 serial number and pink one with 000047514512 serial number. I use the following bash script to access the cameras:

#!/bin/bash
PINK_CAM_ID='000047514512'
BLACK_CAM_ID='000041076602'

while test $# -gt 0; do
  case "$1" in
    -b|--black)   REQ_CAM="$BLACK_CAM_ID";;
    -p|--pink)    REQ_CAM="$PINK_CAM_ID";;
  esac
  shift
done

## Picture filename:
FILENAME="NIK`date +"%Y%m%d%H%M"`.jpg"

## Scan all attached cameras:
while read PORT_ID 
do 
        ##echo $PORT_ID 
        ## -n means string is non-empty
        if [ -n "$PORT_ID" ] ; then
                CAM_ID=`gphoto2 --get-config serialnumber --port $PORT_ID | awk '/Current:/ { print $2 }' `
                if [ $CAM_ID = "$REQ_CAM" ] ; then
                        REQ_CAM_PORT="$PORT_ID"
                        ##echo "*** Req Camera ID: #$CAM_ID."
                fi
        fi
        
done <<< "`gphoto2 --auto-detect | grep usb | awk '{ print $6}'`"


if [ -z "$REQ_CAM_PORT" ] ; then
      echo "*** Error: Camera $REQ_CAM not found ***"
      ## sent a SMS cf http://pinkaccordions.homelinux.org/wblog/sms_alerts_with_google_calendar.html
      sms_reminder.sh
      exit 1   
fi

## reset the USB device
REQ_CAM_PORT_DEVNAME=`echo $REQ_CAM_PORT | sed 's/^.*://' | sed 's/,/\//'`
usb_reset /dev/bus/usb/${REQ_CAM_PORT_DEVNAME}

LANG=C gphoto2 --port "$REQ_CAM_PORT" --force-overwrite --set-config flashmode=1 \
   --set-config d002=4 \
   --capture-image-and-download --filename "$FILENAME"

## reset the USB device again
usb_reset /dev/bus/usb/${REQ_CAM_PORT_DEVNAME}

Property d002 sets picture resolution (4 means 2592x1944).

Value 1 of flashmode turns-off flash.

It seems that without usb_reset there are problems with battery charging (why?)

A620 powered with CA-PS500

A620 (side view)

I would like to remote control a still camera via gphoto2. After consulting a  list of supported cameras I bought (used) Canon A620 from Allegro (local Internet auction site, sort of E-bay).

This camera has many great features (I suspect even too great as Canon stop producing cheap cameras of this sort): viewfinder, retractable LCD and can be powered with Compact Power Adapter CA-PS500 instead of batteries (an important feature in my project). The plan was simple: connect camera via USB cable to computer and power it with PSU. Capture photos periodically with gphoto2:

 gphoto2 --auto-detect
     
 pi@raspberrystar ~/bin $ gphoto2 --auto-detect
 Model                          Port                                            
 ----------------------------------------------------------
 Canon PowerShot A620 (PTP mode) usb:001,006    

So far, so good.

Now, I tried to capture a photo:

# one shot without flash, download the file and store in a file named as: GPHyyyymmddhhmm.jpg
LANG=C gphoto2 --set-config flashmode=0 --capture-image-and-download --filename "GPH%Y%m%d%H%M.jpg"

As the creation time is wrong (due to camera wrong clock) I modified the above as follows (note that touch is used to adjust file's timestamp):

#!/bin/basg
FILENAME="GPH`date +"%Y%m%d%H%M"`.jpg"

LANG=C gphoto2 --set-config flashmode=0 --capture-image-and-download --filename "$FILENAME"
touch "$FILENAME"

Unfortunately there are problems: I am able to remotely capture only one photo. Next remote capture try results in an error and the camera has to be hard reset (with power on/off button). The problem is reported by others too.

BTW: when I connected the camera to my PC the reliability is much better (but seems not perfect---I experienced camera disconnection too.)

My first try to resolve the problems was to update gphoto2 (raspbian contains version 2.4.14 of gphoto2).

Compiling newest (march 2013) version of gphoto2 on Raspberry Pi

## optionally remove old version (there are no dependencies)
apt-get remove gphoto2

There is no need to remove gphoto2 as compiled one will be installed in another directory (/usr/local/ vs /usr/).

First install/compile the necessary packages:

apt-get install -y libltdl-dev libusb-dev libexif-dev libpopt-dev

## Download and install newer version of libusb 1.0.11
wget http://ftp.de.debian.org/debian/pool/main/libu/libusbx/libusbx_1.0.11.orig.tar.bz2
tar xjvf libusbx_1.0.11.orig.tar.bz2
cd libusbx-1.0.11/

./configure &&  make && sudo make install

## Download and install newer version of libgphoto
wget http://garr.dl.sourceforge.net/project/gphoto/libgphoto/2.5.1.1/libgphoto2-2.5.1.1.tar.bz2
tar xjf libgphoto2-2.5.0.tar.bz2
cd libgphoto2-2.5.1.1

./configure &&  make && sudo make install

Download and install newer version of gphoto2

wget http://downloads.sourceforge.net/project/gphoto/gphoto/2.5.1/gphoto2-2.5.1.tar.gz
tar xzvf gphoto2-2.5.1.tar.gz
cd gphoto2-2.5.1

./configure &&  make && sudo make install

## run ldconfig
sudo ldconfig
gphoto2 --version
gphoto2 2.5.1

Copyright (c) 2000-2013 Lutz Mueller i inni

BTW compiling gphoto2 on my fedora 14 box requires to install libtool-ltdl-devel popt-devel first:

#configure: error: cannot compile and link against libltdl
#libgphoto2 requires libltdl (the libtool dl* library),
#but cannot compile and link against it.

yum -y install libtool-ltdl-devel popt-devel

Upon installing above two packages, the compilation of libusb, libgphoto and gphoto2 proceeds smoothly.

Unfortunately installing new version of gphoto2 did not help.

The problem will be further examined...