impose jpg over jpg?

[Anon]

Does any-one know if it is possible to impose a jpg image over another, like a layer in Photoshop, but resulting in one new jpg image?
And while I'm at it, can I via PHP adjust the resolution of an image according to resolution parameters, NOT according to size parameters?

Thanks all,
Andre Q

[Anon]

I might be wrong but as I understand PHP can handle only basic resizing. You should use imagemagic or gimp for something like that.