IIIF Server - image format in manifest


I’ve found some problems testing many different IIIF clients where some of them are not able to open some omeka media.
Going deep in that issues I’ve found that the problem depends on the format field value in the metadata of the media.
In fact I saw that when I load by Tiler a tif image instead of a jpeg, even if the tile version of the media is made by jpegs, the format stored in metada is “image/tiff” and this seems to be the reason why those clients fail.
If I force that format to image/jpeg, those IIIF clients work as a charm.
So I’m wondering if “image/tiff” is incorrect for those tile images coming from a master file in tiff format, and if the right image format for a tile image is always “image/jpeg” indipendently from the original master file format?