Randomly fill a picture with certain items

Creating less than all possible combinations could raise some potential problems. 

Because if one were to combine the elements purely (pseudo-)randomly each turn it might happen that some elements in some of the groups do not get used at all or that the same combination arise more than once. 

So an approach with a restricted randomness might be called for. 

Have you seen this thread yet? 

https://community.adobe.com/t5/photoshop-ecosystem-discussions/combinaison-de-calques-sauvegardé-saved-layers-combinaison/m-p/11376943#M357169

As others mentioned, scripting is the way to go, and it really wouldn't be too hard. You have a list of files to insert. On your main file, you use the eye dropper tool to sample the color of a base layer. By the color you get, you make a switch in the code to select one of your files that best matches the color you sampled. To get the sample point for the eye dropper tool, you use the random feature in javascript to generate the X and y values. The attached is a simplistic example. Only grayscale was used to select one of 4 images. The more gray the base was, the wider the random range.

What is this actually about and how frequent is the task? 

Can you provide screenshots (including the pertinent panels) to clarify the procedure? 

Where do the »items« exist? Separate files, Layers in the file, …? 

As @Mylenium pointed out Scripting seems like the reasonable approach but the prudence of this depends, amongst others, on the frequency of the task. 

Unless you get into heavy scripting with the conditions defined in the code I can't see a way to pull that off. this is way beyond simple datasets, actions and basic scripts. Unless you literally have to do this hundreds of times, it's not worth spending the time to develop a script and 25 variations realyl sounds liek you could do it fast enough by hand. Trying to automate this would be like calling in a helicopter to lift a chair...

Mylenium