Poor image resolution for blog posts on ipad & iphone 6

Hi!

When viewing blog posts on certain platforms, the default page view reveals images with low quality resolution. When clicked, the image resolution for pop-overs on these same images, however, have the correct (good) resolution.

These issues were detected when viewed in Safari on iphone 6 and ipad (model mc769ll/a). There is no issue when viewed on a PC browser, nor does the issue exist on an iphone 6 (safari).

Any idea as to what might be going on here?

Thanks in advance for your time!

Cathy