Is there a way to check if the HD textures of Skyrim are correctly loaded in the game? I installed them without an error, but I'm not quite sure whether they are actually active, as I can't really see a difference to earlier.
First, make sure that in Skyrim's options (Skyrim launcher > Options > Advanced...), Texture Quality is set to 'High'. That should make the difference between textures with and without the HD Textures DLC more pronounced and noticeable.
The HD Textures DLC currently has a noticeable visual bug on certain items in the game, like the 'glowing' firewood and the purple wooden meat chopping block.
If you see any of the glitches in the 'Before' part of the images here, you'll know you have the HD Textures DLC installed and loaded properly (screenshots are from the HD Textures DLC Fix mod page):
When you are on the loading screen click the 'Data Files' menu option instead of Play. The HD Texture packs (And any other mods) are listed on that screen. If they have a check box on them then they are active.
In regards to the HD textures, its most notably active by the increased loading times. Also, you can see the difference if you stand still in the game.. Most motion makes the higher quality textures not so much better than the normal quality textures the game came with.. Great for screen caps, not needed so much for normal play... in my opinion of course.
EDIT: If your 'Data Files' menu option is not available, I found a forum post with other people having that issue and this resolution seemed to work for most people: