I wanted to run Image Processing and 4-5 different sensors on a single Rasberry Pie Board. So what board should be sufficient for the work ? I couldn't choose as I am new to IOT and have very little knowledge Rasberry pie
You can try it out by buying a Pi Zero W to test the requirements you need since they are very cheap.
Then after you ascertained your requirements go for what you need. Stick with the Zero or get a more powerful one.
I believe the Raspberry Pi 3 should be able to do what you want but I would recommend that you get a Raspberry Pi 4 with 2GB at least. That way you have both the processing power and the memory to run almost anything you throw at it Besides, if you then decide to re-use the Pi on another project, you know you have the power for it. The only drawback is the Pi 4 huge power demand of a 3A PSU while the 3 needs 2.5A and the Zero W needs 0.3A (this is just the boards without any sensors)