Method to batch convert images to same dpi

So you want to change all of the images to the same pixel dimensions, right? Unless they are all the same size ratio, it can't be done automatically. If you can change them to the same pixel dimensions they will have the same ppi.

However, you can export them out of your Photos library using a custom export size and set the maximum pixel dimension to WXYZ pixels. That way they will all have the same maximum dimension and be close to the same ppi. Landscape will have a width of WXYZ and portrait image will have a height of WXYZ.

They would fit more uniformly in a PDF document.

In the context of your computer, and pdf or image files, dpi is meaningless.

Dpi stands for dots per inch. That's a measure of the density for a printer. As there is no printer involved, dpi has no meaning.

You can use dots or pixels interchangeably. It makes no difference. The key word is "inch". Basically it makes as much sense as asking for the weight of a jpg in ounces and pounds.

An image has a fixed number of pixels. My camera produces 24 megapixel images. 6,000 on the long side, 4,000 on the shower side that 6 x 4 gives 24 megapixels. Note that there are no inches/feet/metres involved. It a calculation of the number of pixels in the image.

Now if you go to print, what size paper will I need? That's where the inches come in. At 300dpi the image would be 6k/300 or 20 inches on the long side. At 150 dpi it would be 40 inches on the long side. At 600 dpi it would be 10 inches on the long side. The inches are only relevant in printing. Those figures for you quote for dpi are merely notional in the purely digital world of your computer, where there are no inches.

So, no, most people wouldn't understand you.

https://www.rideau-info.com/photos/mythdpi.html

or

https://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#:~:text=The%20misconception%20about%20resolution%20in,to%20layout%20on%20the%20web.