SNA is an old image format used on ZX Spectrum computers for storing Mirage Microdrive snapshots. ZX Spectrum was an incipient brand of home computers released in the early 1980s and discontinued a decade later. Some of its rival brands on the European market included the Commodore 64 and Amstrad CPC. SNA images are very rare at the moment, so conversion is probably necessary in case you intend to access such a file.
JPEG JPG PNG GIF TIFF TIF BMP ICO EMF WMF AI PDF EPS PS EPI WEBP WEBPLL JP2 PCX TGA DWG DWF DXF DGN WMZ CGM DRW GBR PCT MIF PLT PCL SVG WPG CIN DCX DIS HRU MTV PRC RAD PIC RLA QRT SGI XBM XPM SWF CAL PSD JXR BPG APNG DDS SVGZ CG4 FLIF