Are there size limits for image operations?

Yes.

For Image Transcoding with SmartVision enabled, the maximum size of images that the SmartVision algorithm will be applied to is 4000 x 4000, or 16,000,000 pixels. Images larger than this will be transcoded to a fixed quality level of 90% by default (this value is configurable).

For Image Adaptation operations, there is an upper limit of 5000 x 5000, or 25,000,000 pixels. If the area of the requested image would be larger than this limit, the image service just returns the original requested image.