The thread that Lost_in_A2 pointed out is “Looking for info on ICRX- Island Creek Corp”.
For your reference, I will describe the method I use. If you know the reporting mark, the first step in your investigation is to access the list created by Ian Cranstone (website). There you can find out the owner and period of ownership. The period of ownership is particularly important. If it is different, the owner have changed.
Next, look at photo aggregation sites. railcarphotos.com, as pointed out by maxman, is well-known, but another one, rrpicturearchives.net (website), is also useful. There are also many other people who publish photos individually.
If you make full use of search engines, you can find valuable information you never expected. Good luck.