Hi, Lochranraj
No, it has nothing to do with a premium version.
In an effort to prevent the Image Optimization Server from getting too bogged-down with requests, we’ve implemented a credit system.
Each site is assigned a level. Levels start at 1 and increase as the site continues to frequently use the service. Currently there are five established levels, and each level has an assigned number of image optimization credits. Credits represent the maximum number of images you may currently submit for optimization. Credits regenerate at the completion of an optimization cycle.
So, if you have 99 credits, it means that is the largest number of image groups you may submit right now. After the images are processed and pulled back into your system, you get the credits back and may request another 99 image groups.
You can learn more on our wiki.
Hope this helps!
