Raspberry Pi £25
SD card £5
Edimax usb wifi adapter £10
Power cable £5 (although you probably already have one)
Raspberry Pi HD camera module £20
Raspbian OS Free
Fswebcam app Free
get the above, install the OS (dead easy and effectively 2 mouse clicks, install fswebcam (type “sudo apt-get install fswebcam”), run the app (type “fswebcam -d /dev/video0 -l 600 -s 10 -r 640×480 %m-%d–%h-%m-%s.jpg”)
This will take a picture every 10 mins and save the image with the date and time. You can change the period between pics by changing the “-l” setting which is the number of seconds between pics).
You would just need to put the whole thing in a weatherproof box. You could also run it off a battery. Total cost probably less than £100.