You say you know how to create it, so most of the work is done. In Description.ext where you define the rcs picture there will be a definition for x and for y. These determine where the picture will be placed on the screen.
x measures the distance in from the left and y the distance down from the top. The numbers range from 0 to 1.0 In other words they are measured in fractions of the screen. Here is an example:
class LARCHEMAP
{
idd = -1;
movingEnable = true;
duration = 5;
controlsBackground[] = {};
objects[] = { };
controls[] = {PICTURE1};
class PICTURE1 : RscPicture
{
x = 0.5
y = 0.5
idc = -1
w = 0.4
h = 0.37
style = ST_PICTURE
colorText[] = {1, 1, 1, 1};
colorBackground[] = {0, 0, 0, 0};
font = "TahomaB36"
SizeEX = 0.04
text = "LarcheMap2.paa"
};
In this case the top left of the picture is in the centre of the screen (x = 0.5 and y = 0.5)