First, nice stamp, thanks for sharing.
Second, to get the best answer from the most people, post just a couple stamps in their own topic (start a new topic) asking for help to identify, and then when some identification has been made, edit your first post in that topic to change the topic title to include the country name at least.
This is for future people (and us) to be able to find the topic when searching and to help other searchers on SCF and Google find info about it / them.
Try to put stamps in their proper forum area if possible, US in US modern or old, etc, this helps a lot because people sometimes only collect and are expert at a certain area or country or era and that will help with identification and info.
row 1 - Greece or Greece area, cancel a variant of a bridge-type cancel (shaped like a bridge)
row 2 = Netherlands (Holland) Queen Wilhelmina , cancel year date 1904 (which helps you to date the stamp usually) (Modern stamps are harder this way as people can use stocks of stamps on mail because that way they get the best return on them instead of selling). There is probably a special name for this type of double ringing cancel but unknown at this time to me.
row 2 Belgium, King Leopold, cancel 1893 CDS (Circular Date Stamp) type that is SON (Socked On the Nose).
row 3 both Romania, both nice cancels of a railroad type, usually called RPO (Railway Post Office) or TPO Travelling Post Office, No44 might be a train number or just a post office depot number.
Cancels are a world of their own and change as the years go by or even have different types of the same one occurring at the same time frame. there are sometimes specialized catalogues just for these cancels.
row 4 US, not sure on anything about these, Washington, perfs cut close lowering the value to 10% if that, with a marvelous target cancel (concentric rings) and Franklin.
row 5 = Great Britain (Queen Victoria), with a fiscal (financial revenue) type hand written cancel. Knowing your monarchs helps narrow down the era when a stamp was used and where it is in a catalogue, good for selling also. GB is the only country to not have to have to state their name on the stamps, nowadays just a silhouette of the Queen (Queen Elizabeth II).
tow 5 US 5c Washington, cancel interesting, note that in classical (pre 1940) eras of stamps the UPU Universal Postal Union, had rules that countries followed to help aid the movement of mails. One was the colours of certain stamps. Blue was usually for an international rate.
row 6 There are those possible Greece stamps again (from row 1) but now I see the overprint along the bottom, these might be many countries that use a Cyrillic or similar script = so I don't know these.
row 6 China (mainland), the guy is Sun Yat Sen, Shanghai cancel, a British treaty port I think, so cancel is in English and you don't have to learn a version of Chinese today.

row 7 = there is no row seven.
So, if no one else answer s you on the possible Greece (probably not) stamps, go and post them in a separate topic by them selves.