Can I use my own SD-Card,...mine is of a different size?
SD-Card’s do only come in one size. If it does not match the picture to the right it is not an SD-Card.
It should for that matter also have the SD Logo.
The Secure Digital standard was introduced in 1999 as an evolutionary improvement over MultiMediaCards (MMC). The Secure Digital standard is maintained by the SD Card Association (SDA). SD technologies have been implemented in more than 400 brands across dozens of product categories and more than 8,000 models.[Wikipedia]
At this time all the leading digital camera manufacturers used SD in their consumer product lines, including Canon, Casio, Fujifilm, Kodak, Leica, Nikon, Olympus, Panasonic, Pentax, Ricoh, Samsung, and Sony.[Wikipedia]. Almost all No-Name or discount name brands use SD-cards only due to lack of access to other memory card types.