add a merge_images function
add a merge_images function
bthirion/nipy,bthirion/nipy,nipy/nireg,nipy/nipy-labs,bthirion/nipy,alexis-roche/nipy,alexis-roche/niseg,alexis-roche/niseg,arokem/nipy,nipy/nireg,bthirion/nipy,alexis-roche/register,arokem/nipy,alexis-roche/nipy,alexis-roche/nireg,alexis-roche/register,arokem/nipy,alexis-roche/nireg,alexis-roche/register,arokem/nipy,alexis-roche/nipy,alexis-roche/nipy,nipy/nipy-labs