Everything is contained in the RailPro Assistant manual, from page 24 (creating images) and page 9 (loading pictures). I could type out an abridged version but instead I recommend you watch Kevins video as it covers it all.
https://rpug.pdc.ca/index.php/topic,571.0.html.
I suspect you have actually already created the images themselves but if not, or if they are not in the correct format and you don't have the image editing software that Kevin uses in his video there are other methods as well.
PDC RailPro Bitmap Builder:
http://pdc.ca/rr/RailProBmp/How to resize photos for use with RailPro using MS Paint:
https://rpug.pdc.ca/index.php/topic,194.0.html.
This should get you started. If for some reason you just can't get the image format right no matter what you do I'm sure someone here would be happy to convert them for you if you ask.
If you want to share your pictures with others here just upload them to the files area.
- Tim