A very useful way to organize images is through creation of an image library. The system we suggest uses a number ordering by market/industry and perhaps also by product if appropriate. Choose which is best for your use and keep one for people and site images We then draft a brief description which is searchable for easy retrieval. Use both high and low resolution images so internal staff can access the res suitable for use and not place huge files in say PPT presentations. (bogging down the file needlessly)
The library system # becomes the perfect reference. Client, and agency partners know exactly which image you may want in a particular piece and there is no question that the retouching was done on the one in the system.
Be careful not to include any images that are rights managed. Their use needs to be monitored carefully to track against what was purchased. We generally add royalty free images but note them as such so there are no surprises with lack of exclusivity.
You may also find it handy to add commonly used graphics such as diagrams or line art.