Zipping files is the best way to compress file sizes while sending them through emails, but each and every time you receive a compressed attachment in the form of zip or rar files, you need to uncompress them to view the attached files.
Softwares like WinRAR and WinZip do have support for viewing text files without unzipping the, but to view images in a compressed file you need to extract it before you can view them.
Zipeg is a freeware alternative to popular paid softwares like WinZip and WinRAR, but unlike other free alternatives Zipeg has a really nifty feature which allows you to preview compressed images without having to unzip it to your computer.
Zipeg currently supports various popular compression formats including ZIP, RAR, 7z, ARJ, LHA, TGZ and TAR. You can preview the images instantly or open them in a external application, by clicking on the preview button.
Zipeg is absolutely free to use and can be downloaded for Windows XP, Windows Vista and Mac OS X.