I am wondering how to make all the thumbnail images of excerpts on the blog roll the same size. Most of them seem to be the same, except for the image on the last post on front page (i.e. Basic Principles for Natural Short Curly Hair).
The only solution is to use all images with similar aspect ratio. The thing is that all (most) of your images are rectangle in landscape but this one is square. WordPress tries to crop images as little as possible, so it crops only height or width (noth both) to make it fit defined image size.
For this one image you could add white (transparent if PNG image) space on the sides to make it rectangle and that way WordPress will properly resize and crop your image. No code solution is possible.