There's a lot to cover here.
First the scanning. The scan results in a picture (might be .bmp or .jpg) with a certain number of pixels (x and y axis). If a photo is 10 x 15 cm, that can result for example in a picture of 2000 x 3000 pixels (the exact numbers depend on the settings of the scanner). But if it's a 9 x 13 cm it will never become 2000 x 3000 (at best 2000 x 2888), and if it's an old square 10 x 10 picture it might become 2000 x 2000 (or whatever). That's the aspect ratio. If the aspect ratio of the source is different, it will have a different aspect ratio when displayed. The only thing you can do about that is to use a photo editing program to cut off everything outside your own preferred aspect ratio for each picture that differs.
Then we have the display size. A lot of programs on a PC have settings to control that. Say the original size: a picture of 2000 x 3000 pixels is shown only partially (with scrollbars) if your monitor isn't 2000 x 3000 pixels (it isn't). Or the best fit with black to fill up the screen. So a 2000 x 3000 picture in portrait mode will be shown with 1080 pixels vertically if your monitor is 1920 x 1080, with a lot of black on the left and right side.
So the next thing to consider is what the TV does when the pixels of the picture are not exactly equal to the pixels of the screen. There might be a fixed way to do it defined in the TV's firmware, or it might have a photo viewing app that lets you control it.
So depending on those factors you might need to use a photo-editing program to edit all pics to the same number of pixels (x and y). That's the only sure thing: if the x and y are the same, they will be displayed in the same size.
Adding a DVD-player to the mix adds more uncertainty, because it has it own settings and options. There are quite a lot of smart TV's at the moment that can display pics from a USB-stick, an external hard disk or your home network without a DVD-player processing them. That might be easier.
For a slide show, there's also the slide show software. Is it an app on the TV? Is it an app in the DVD-player? Do you use Powerpoint on your PC to produce an avi-file of flash file that can be read directly by the TV? Or do you put it on Youtube to view it with the Youtube-app on your player?
And imagine the issues that you encounter if it finally works on your Sony player and TV, and you give the DVD to somebody else with a different player and it looks totally different, because you relied on some feature of your player app that doesn't exist on his Samsung player.
Yeah, it's difficult and time-consuming.
I have an Epson GT 15000 scanner. I also have several thousand photographs I would like to digitalise but I'm already in trouble because I can't work out how to get the photographs to show all the same size when they are viewed on the TV.
By that I mean that when I scan the different size photographs from 2.5 X 3.5 inches to 4 X 6 they appear in different sizes when I open the folder they are in.
I'm not sure what effect that will have if I ever get to the building a slide show stage.
I know that I will need to burn the results to a CD or DVD because want to view the photographs through a DVD/CD player on a TV.
Actually, I'm don't even know if it is a DVD or CD that I should use to put the slide show on.
I think that the Epson GT 15000 is up to what I want to do but would anyone care to comment on its software and if that is up to what I want to do.
If it is not should I be looking at different software?