Using a map image to set icons on coords (read to understand)

Hello,

I wan't to use a selfmade map on my website, which I can put icons on from things that are there, but the hard part is, how can I convert it to coords, like the X coord is : 10000 and the Y is 10000
So when I put a icon or marker on X = 230.01 , Y = 340.023 or something it will give a marker on that place.
And I gues I also have to make a scale of the map or something, I don't realy know how to explain it, but if you see what I understand maybe someone knows what java,html or php function,tutorial,class I have to use for this.
Thanks.