Pairing iPad /iPhone

Bluetooth pairing an iPhone and an iPad is not supported. 

If you are attempting to use Handoff/Continuity or AirDrop, that does involve Bluetooth but the devices are NOT paired; Bluetooth just needs to be on and the devices in range of each other. The following may help with Handoff/Continuity issues: Work seamlessly across all your devices - Apple Support

And see the information in: Bluetooth: Why can't I pair my iPhone or … - Apple Community

One option is to sync all photos on both devices by using iCloud Photos. All of your photos will be on both devices and on iCloud. See: Set up and use iCloud Photos - Apple Support

Another option is to AirDrop photos from one device to the other: How to use AirDrop on your iPhone or iPad - Apple Support

Another option is to text or email the photos to yourself.

What, specifically, are you hoping to achieve by pair your iPad and iPhone via a Bluetooth connection?

Whilst it is technically possible to do so, be aware that Bluetooth pairing between an iPad and iPhone is generally pointless. If your intention is to use Cellular Hotspot features of your iPhone, this link is optimally achieved using the native WiFi hotspot connection - this being a largely automated process. Hotspot connections over WiFi offer substantially greater throughput, range and reliability.

How to set up a Personal Hotspot on your iPhone or iPad – Apple Support

If you still wish to pair your iPad and iPhone over Bluetooth, you first need to manually enable the hotspot feature on your iPhone:

Settings > Mobile Data > Personal Hotspot > Allow Others to Join - set to ON

Next, Bluetooth for both the iPad and iPhone must be placed in Discovery mode:

Settings > Bluetooth (accessing this page will automatically place the device in Discovery mode)

Whilst both iPad and iPhone are in Discovery mode, you can mutually pair the devices.

Again, I must stress, unless you have an unusual “edge case”, pairing of iPad and iPhone over Bluetooth has no benefit.