I came here for an opinion from someone who had a similar experience. And yes, you can guess from a photo. You don't need a degree in some study to recognize a pimple or when it will clear up. If it is in violation of the forum rules, please tell me why there is even a health section on this forum. If nobody can answer, don't bother even creating it.If you are concerned enough to register on a forum to ask about it then, yes, you should contact your vet. It will be impossible for anyone here to guess from a photo. And anyone who tries would be in violation if forum rules.
I'm sorry if this sounds harsh, but it is for the protection of your dog and the forum.