I also checked permissions, they're completely the same for the images in 'AppData' and outside 'AppData'. I tried to repair Photo app in the system settings, just in case. I assume the problem is in 'AppData' folder.
If I move an image from AppData to anywhere, the 'Delete' button becomes active again. In other folders outside 'AppData' everything seems fine, 'Delete' button is active. I try to delete images in C:\Users\%my username%\AppData\Roaming\ while viewing them in Photos app. My problem is the 'Delete' button in Photo app is greyed out and unclickable.
