Note: There are some limits for attachments. They are displayed when you expand the "Attachments and other options" section, but I will copy them here FYI:
Allowed file types: doc, gif, jpg, pdf, png, txt, zip, tar, c, h, hex, bas, xls, odt, asm, wav, aiff, wma, mp3, flac, asc, ods, xlsx, py
Restrictions: 25 per post, maximum total size 2000KB, maximum individual size 1000KB
Alternatively, you can have images hosted elsewhere and just use the [img] [/img] tags.