This term describes the number of pixels (or picture elements) in the camera’s recording sensor or “digital film” chip. A 1-megapixel chip has a total of one million pixels, which are calculated by multiplying the number of horizontal pixels by the number of vertical pixels. The higher the pixel count, the better the quality of your photos.
Any Digital Camera with 5.0 Megapixel or more is ‘good’ one. For a cam in mobile phone, I would say anything 2.0 or more is good.
Digital cameras can have two types of image zooms: optical or digital. An optical zoom works like a conventional film camera, in that the camera lens increases the image magnification up to its maximum zoom range (i.e., a 3X optical zoom lens magnifies the image by three times the original). In contrast, a digital zoom uses built-in software to increase the size of the pixels, resulting in a lower-quality image. For the highest-quality photos, you should always use optical zoom and avoid using the digital zoom whenever possible.
Anyway, if you can get closer to the subject and shoot, that is always better than either of the zooms. Use these, if you cannot get closer for some reason.