It's become a matter of common knowledge widely accepted that Haeckel's drawings were fraudulent, but it's not at all clear that it's true.
The first thing to bear in mind, is that the picture presented by Portillo above is from a book published in 1874 (
Anthropogenie: oder, Entwickelungsgeschichte des Menschen), the first edition of said work. Microscopy at the time was not what it is today, and embryos in their earliest stages are
small. It was not possible to determine the level of detail we're quite capable of today. What's more, Haeckel was a marine biologist - he hadn't studied all of these vertebrate embyros in detail before drawing them. Some of the images were copied from the work of experts in the relevant field.
Anthropogenie was intended for the general public, created out of lecture notes he used in public lectures. As the years went on, he revised the work as he revised his lecture, adding more detail, clarifying points, and improving accuracy. The pictures of the embryos grow more detailed, and accurate, as each edition goes on. Better microscopes and more available information allowed him to improve his crude sketches.
And they aren't shockingly inaccurate. The picture below is taken from
Haeckel’s embryos: fraud not proven, by Robert J. Richards, which was also the source of all the info in this post (via
Josh Rosensau on scienceblogs). It compares the more accurate drawings Haeckel used in the fourth edition of Anthropogenie, with modern photographs. Considering the equipment available at the time, they're not that bad.