I've reviewed your featured post about licensing terms and I'm still unsure on the answer to my question.
I'm having a hard time finding a solid answer to this question. I see previous questions and answers that are similar to this that mention that if the image is unmodified I must add a credit line. However, when I review the Terms and Conditions in detail, I see that a credit line is only required if you use the Stock Asset in an editorial manner, if the Stock Asset is "editorial use only", or if you use the Stock Asset in an audiovisual production. I see nothing about unmodified images.
Is a typical blog post considered editorial? For example: "Best Time to Visit Mexico" or "10 Best Vacations for Newlyweds".
Editorial use is, when you write an article and use stock images to illustrate it. They are mostly always unmodified. So yes, I would say from what you told that a credit is mandatory here.
(Disclaimer: As always with licensing, this is my interpretation of the rules. I think they are correct and advice is based reading and interpreting the license terms and on fair use for both the buyer and the artist/stock company, but I can not rule out that my interpretation is wrong. I'm not an Adobe employee)
ABAMBO | Hard- and Software Engineer | Photographer