When I tried to load my second package on Unity Asset store and I couldn’t get images saved as .png, I uploaded png, but eventually they turn into jpg. That package was declined about couple of times because some of my images saved as jpg: when I click on loaded image and selec ‘save as’ it wants to save it as jpg, the other images as png. I tried to explain problem in comments to packages when submitted it, but still get the same answer. I tried to create new package, but it happens again. Key images have that problem.
You’re not understanding the issue. You don’t just change the image type while uploading to Unity. You need to actually convert the file in an application like photoshop or gimp2. Just changing the filename does nothing except irritate people when they find out you’re incorrectly naming your jpeg images as png.
Plus I think it is unlikely you’re being rejected due to key images. The restrictions on jpg images in the submission guidelines are regarding textures within the package itself you are uploading.
I converted key images to png and checked format in file properties. Probably you right about images inside of package, thanks.