You can measure the width of the road on Google maps, but for most roads if you are not completely over the line you are too close. Difficult to say on those pictures, but if you can post the location and make of car it could be estimated. Having said that if police have decided to prosecute, then it must look close, and I imagine it would be hard to defend unless there is something really screwy going on with the camera angle. The cyclist will have been passed lots of times on that ride alone, and will know which feels close / dangerous and worthy of reporting.