Modern phones have really good cameras and in most cases picture quality is absolutely fine for our purposes.
Remember that each item in your guide may have many images. So, aside from the image of the whole object you can use photographs showing some parts of the object.
Make your own pictures and avoid using images from the Internet or be very careful – check the copyrights. Here is one article on using Creative Common licensed photographs //creativecommons.org/examples
Images for izi.TRAVEL platform should be of 3:4 ratio. However, this is not a big problem if your original is of a different ratio – you can crop the image while uploading.
Make sure you have good lighting. The best is to make pictures using daylight. Do not make photographs facing a sunlight or lamp. Do no use flash – it’s guaranteed way to get glare on the picture.