I think the footprint images could be used to denote groups of footprints for similar species.
IE: You get a text paragraph saying "the footprint is medium sized and has five toes". You look some more and find "the footprint is medium sized and has five toes."
Problem is one is humanoid and the other is ape-ish.
If you show a generic humanoid foot or a generic prime ape foot... the player will be like "okay I'm following that Chimp that stole my food; so I'll ignore anything that doesn't have the prime ape foot print". Alternatively if they are following a dwarf, they will ignore anything but humanoid prints. They might have to study the description more to tell specifics (ie, dwarf prints are medium and broad; humans are medium), but the generic foot prints could act as a visual filter. The player sees the image and knows whether or not they could just skip the description. The description can go into more detail for missing toes and other info that might help the player.
That being the case, the images could be limited to groups that make sense. IE: bipedal humanoid (human, elf, dwarf), padded quadruped (dog, cat, wolf, tiger), rodent trail (rat, mouse), drag trail (snake, alligator, zombie whale), talons (chickens, owls, turkeys), hoofed quadruped (boar, goat, horse), bipedal humanoid with shoes (human, elf, dwarf).
A couple more than that as well. Some special creatures could have unique foot prints for flavor (ie: dragons), but every single animal species shouldn't require a unique footprint.
I could see the value of using the graphic as a quick and easy way to determine whether or not you want to read the description in depth thus saving you a couple seconds. That may not seem like a good reason, but imagine someone lead you through an area trafficed by tons of creatures. You'll love having a simple indicator to help you out.