Adobe Premiere Pro: Required Image Size?

Hello, whatever the software, you will be forced to use the 4:3 format in your project if you have 4:3 photos, because if you keep the photos in 4:3 and the project in 16:9, the image will be distorted and stretched. The solution is to crop all the photos to trim them, but not all will be able to handle the cropping; if there are characters in the foreground, they might end up with their heads cut off.
Adobe can help you with this cropping with a slight zoom to make the bars disappear, but I am not familiar with it.

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Hello, an image size refers to its weight in KB, MB
there is its ratio in pixels, meaning a relationship between width and height, for example in 4/3 720x576, 16/9 720x1280, 1920x1080 for better performance. The size has no impact on the ratio, but a photo of 200KB will be less detailed, less sharp than one of 2MB.
The quality of the photo will not be enhanced by the finalization of the film; the software cannot create details that do not exist.
An optimal size for a photo to achieve a good result on a film that can be viewed on a large TV, in my opinion, requires photos of 1MB to 2MB, making the film in 4/3 and 720x576 or with a higher resolution in 1920x1080, extension .mp4 or .mpg2
Did I make myself understood?
Software with text animation functions (amphase)
All “consumer-grade” editing software starting from €60 offers a multitude of templates: "Pinnacle Studio", "Magix Deluxe", "Sony Vegas", "Cyberlink".
There are free ones on your computer, like Windows Movie Maker, which will also create a simple presentation with titles and some effects.

“Donkeys change their minds, not fools.”
Remember to mark your message as "resolved" if that is the case.