In order to do what you want you will need to convert your layer into a vector layer using the 'raster to point' tool (I can't remember which toolbox this is under - I think it's the 'conversion' toolbox, but you can just find it with search).
When you convert it make sure you select your classified value under the 'field' option.
You should then have a point layer with your classified value as one of the attributes. To set you bmp image for each cell, right click the layer and go to properties and then the symbology tab. In the column on the left headed 'Show:' choose categories, select your classification under the value field and then click 'add all values' at the bottom.
Now you just need to change the symbol for each class to your desired image. To do this double click on the symbol for the first category, this should open the symbol selector window. In here click on 'edit symbol'. In here change the drop down at the top from 'simple marker symbol' to 'picture marker symbol' and this should allow you to select your image for that class.
You may need to play around with the size settings a bit to get it just how you want it, but if you repeat that for each category then hopefully it will do what you want!