Trying to figure out which book this is!
Thanks for asking!
There are a lot of animal detective series out there, so if I'm wrong about this one let us know and we'll keep trying, but I'm willing to bet it's the Geronimo Stilton series. The art style has changed a bit over the course of the series but bold fonts, colors, and pictures in the text are a pretty regular feature.
If not, let us know, and the search continues! Thanks for using AskOPL!