Re-writing answer adhering to Stackechange`s guidelines:
"trimming" an image is is quite easy, it takes just two linux commands -
First, determine the size of the actual partition of your interest inside the image
Second, trim it.
Be sure you have read-write permission to the disk partition containing the image file of you interest (i.e. if you are a windows user and are using a live linux distro just for this operation, mount your windows partition with r/w permissions) then run the command:
$ fdisk -l /filelocationofmyimage/myimage.img
this will return information in the format
Device Boot Start End Blocks Id System
Write down the highest end block value amongst the partition(s) of your interest contained in the image file lets call this value mypartendvalue
Trim the image running
The "+1" is needed since blocks are counted from zero and the parametrs we are passing to truncate is a size so without the +1 we`d lose one block.