Might I suggest that mounting a TV over a fireplace isn't the best idea because the viewing angle is typically off. Ideally you want the TV mounted so that the middle of the screen is roughly at eye level from a seated position.

If you use the fireplace, the heat may have a negative effect on the electronics of the TV as well.

Thanks but much of the viewing will be from a standing position as it is visible from the kitchen. We have our family room flat panel mounted fairly high on an adjustable mount and like it just fine.

As far as heat from the fireplace - this will be recessed into the wall and have a fairly substantial mantel to protect it so heat really isn't a concern.

I'm just trying to find a way to slide a picture over it to hide it.

Not really what you wanted but it's fun anyway.

Here is a link that might be useful: Winscape

Take a look at actuator-based designs like the one linked below. You'll need to see if there is enough clearance between the mechanism and TV.

Here is a link that might be useful: Tv Lift kit

What we were looking to do was to have the TV fixed in place and the picture frame slide up and down but thanks anyway.

We ended up not putting a TV in that location after all.

I realize you changed your TV's location but did you ever locate a picture frame lift ? I can only find the TV lifts.

You could get some long ball bearing drawer slides and slide the pic out of the way.

Neither the TV nor the picture probably belong there :)

So a couple of other ideas you might want to try. Samsung makes their Frame TV that shows your favorite artwork when not in use.

https://www.samsung.com/us/explore/frame-tv/highlights/

Only downside is there is a separate 14.3" x 4.5" x 1.2" IO box that needs to be hidden out of view somewhere and still connect to this TV. You could actually hide the IO box in the recess and then install the frame TV over the top assuming the mounting hardware will reach past the edges of the recess.

Another option to look at his Seura TV which is the same idea but a mirror when not in use.

https://www.seura.com/products/smart/

They have two flavors-- a bathroom mirror type where even at 2-3" from the mirror you cannot see the TV. The TV quality is not as good but a better mirror. The second is the Living Room mirror type where you cannot see the TV when standing 3ft or farther from the TV. Not as good of a mirror but a better quality TV. On this one be careful on the 4k side as they are 4kUHD compliant but not HDMI 2.0, HDCP 2.2, or HDR compliant the last I checked. That's a bunch of tech compliance but bottom line is you want all that in your TV if you want the very best picture available these days.