How Can I Remove Someone's Picture From A Photo Without Keeping Any Trace That The Photo Has Been Edited? Also, How Can I Change The Background Colour?

You need to install adobe photoshop in your pc. Adobe photoshop CS2 version is very well in dealing with editing photos. Select the cutting tool from the toolbar. Open the picture. You now need to cut the photo from background. Little practice is needed in this area. Now zoom in the photograph , so that you can clearly see its edges. Now trace the cutting toolbar on its edges which you want to separate from the whole picture. When you are finished, press Ctrl + c .
And open a new window ( file >>> new).

Here paste the picture which you have copied. Now you will see the picture being pasted which you have cut from the previous picture. Also you can now change the background colour by using the layer options.