I received this iPad from my deceased uncle and would like to keep the pictures but add my apple id

Key question: do you have his Apple ID and password? Can you get into the phone? If you can:

If he has signed into his ID on a device then fortunately when you sign out of that ID, do not erase the device, then sign in with a different ID, it asks you in most cases if you wish to merge the data from the two IDs on your device. Say yes and later delete individual items from the other ID that you do not want. Note, in How to save apps and progress on one Appl… - Apple Community a Community Specialist says, "you will not be able to transfer the meta data from one Apple ID to another. Once you switch to another Apple ID the information associated with the old Apple ID will be gone except for physical content on the device like photos and videos."

If you do not have his log-in information, read about how to request access to a deceased family member's Apple accounts; click here --> How to request access to a deceased family member's Apple account - Apple Support

You have the passcode for the iPad. You need the password for his account to be able to disable Find My. For that you need to apply to Apple. Either that or Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not state what currently constitutes proof. Prior to this new online service Apple typically required the original receipt issued by Apple or an Apple Authorized Reseller and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership).

Apple recommends you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support

Sorry, I meant get into his iPad? I am assmuming you probably can't, in which case you will have to go the legal route as outlined in the second document.