There are a lot of cameras out there, so one thing to consider is cost. I'm in a similar situation. The things you need to consider most are not that you can get a picture of the intruder or be able to see them ripping you off when you're not home. Even with that knowledge what are you going to do about it? By the time you can do anything they will be long gone. So will your plants. What you need is an immediate means to deter them. Basically scare the "heck" out of them so they take off with their "tail between their legs", or make it very difficult for them to break into the shed.
I haven't decided on a means yet, but will soon. Lucky for me its legal to grow 6 plants here so I can get a system that sets off an alarm and notifies up to 5 contacts immediately. If the cops or security people come by no big problem but if stealth is an issue then you need to find an alternative.
A friend has a setup that is maybe a bit over the top- but likely very effective. He has 3 cameras that relay video or stills via cell phone so he can identify them before they get in and if they open the door to the greenhouse_ they only way in_ they will get a very rude surprise. He has a trip wire setup that is set to go off if the door is opened without deactivating the "alarm"...instead of a siren the trip wire sets off a 12 gage shotgun blank_ its only about ten feet from the door and is a very effective deferent. Only bummer is you can't hear anything for a few hours afterwards so make sure you don't open the door without disarming it. No buckshot so no real harm. Less than $30 US. I can get the vendors info if you're interested.
You also should not get a wifi setup because the intruder can cut the cable at your box and disable the wifi.... so make sure you get one that provides the warning via cell instead.
