Is it possible to globally move images within posts?

[seo.gops]

With many hundred posts... if an image is posted before the first line within a post - is it possible to move ALL of these images to be after, say the first sentence?

[Shree Vaghani]

IF your image is contained within a clas or ID container, then editing the relevant css can change positioning, yes. If it is not you could see if your css supports a change in padding or margin for <div> or <p> (whichever is containing the images) that might give you what you want. Bear in mind that IF you edit the css for a base element such as <p> it is going to change them all, everywhere.

Different themes allow different levels of templates to be edited which may be another way to do that.