How can I insert a render or a stock to create a signature or a profile banner without having it change the default size that I have chosen for my project?

I.E, let's say that I create a new Untitled project with a 800x600 size and that I insert a picture that is smaller, it will automatically resize... How do I remedy to that?

Any help will be appreciated!

nothing does automatically resize. if using photoshop, just hit CTRL + T and u can resize ur render. make sure to hold shift while resizing, for keeping the proportions

Awesome, didn't know that it was that simple

Thanks, I'll try that.