What’s an economical way to automate one photo per day for a year from a window?

Many of the older Canon A series point & shoots can be highly controlled by use of a free software product called "CHDK" - Canon Hack Development Kit. The features provided add considerably to each camera's functionality.
These cameras are often available 2nd hand at low cost. Lists of suitable cameras are available.

CHDK is immensely capable - you can trigger a sequence of timed stills or video based on movement in selected area, set interval timers, set ISO and extract RAW files on cameras that do not offer the facilities usually & much more.

Start here CHDK Wiki and then this garglabet search will provide ample extra.

SOME OF THE FEATURES: (from the Wiki)

• Shutter-priority (Tv) exposure - via shutter value override feature
• Aperture-priority (Av) exposure - via aperture value override feature
• Shooting in RAW, with RAW Average, RAW Sum, and RAW Develop features
• DNG (Digital Negative) in camera conversion, and USB download options
• Bracketing -Tv, Av, ISO, and Focus bracketing, using scripts, or in continuous or custom timer modes
• Live histogram (RGB, blended, luminance and for each RGB channel)
• Zebra mode (a live view of over and under-exposed areas of your picture) for many cameras
• Depth-of-field (DOF)-calculator, Hyperfocal-calculator with instant Hyperfocal and
• Infinity focus-set, and more
• Battery indicator
• RAW and Video space-remaining gauges with custom low-limit alerts
• USB cable remote shutter release
• Motion-detection trigger - automatically fires camera on motion detection. - Ability to capture lightning strikes.
• Adjust Video quality and size (compression) adjustable while recording
• Elimination of 1 Gig video-size limit (for most DIGIC II cameras)
• Zoom during video function - for cameras without this feature
• Shutter, Aperture, and ISO Overrides
• Ultra-long shutter speeds - at least up to 64 seconds - and longer for supported cameras
• Ultra-fast shutter speeds - up to 1/10,000" and higher
• High-speed Flash Sync at all speeds up to 1/64,000"
• Custom, user-editable visible grids for framing, cropping, and alignment (not all cameras)
• File browser
• Text reader
• Text editor
• Calendar
• Games
• Fully customizable CHDK display, info placement, user colors, fonts in menus, etc.
• Multi-language Interface - CHDK supports many languages
• Custom CHDK User Menu - for instant recall of up to 10 favorite functions
• Scripts execution - including intervalometer, motion detection, etc
  ...

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