Hi all, I hope my question is clear as English isn't my first language.
I've had an issue with images changing size when I open my file. I'll upload an image, change it so it fits what I had in mind, then save my file and close it. All is well. But then, when I open the file, the pictures have changed size! My latest example below:

The cards were supposed to all be the same size, and I've changed their outline so that they can't be seen through the "spreadsheet" because as you can see some of the lines are partially transparent. That took me a lot of time and tinkering and when I opened it today the cards were all different sizes and their outlines seem to have changed which cuts part of the images...
Another example from an earlier version of my work:

Last time I closed that file, the character was on top of the margin and there was no part of him cut. Now he's below the margin and his feet are cut and I can't figure out why!
It's driving me insane because I'm self-taught and everything I work on takes me a lot of time, so opening my file and seeing hours of work wasted for no apparent reason is making my head implose... Please help me understand what causes this and how I can avoid it in the future!