So.. For some reason, I need to design a calendar.

Just throw it together in MS Paint.

I use Thunderbird+Lightning as a calendar, you could try this

U can use adobe ilustrator ou corel draw.
In some sites like sharegfx there are hundreds of calendars templates like u want.
Any doubts send me a PM and I can help u.

why don't you STFG?

I have a feeling Google Picasa knows this trick but I'm not sure, I'll try asap and let you know...

Microsoft Excel.

The PrintShop has a great calendar maker - but it's a little overkill if all you want is a calendar and it doesn't exactly meet the "simple" requirement.

Word should do the trick for you simply enough - insert a calendar object, size it to fit the bottom half of a page and insert a picture into the top half. Or even better use landscape orientation and one page for the calendar, one page for the picture.
I can make a template and send it to you if ya want

Can I be naked on the month of December?

Are you making an achievement calendar to mark all your goals with?

As long as it isn't for commercial use, I'd just find a pre-existing calendar for whatever year, copy the 'bottom' pages with the dates etc, double the height, and insert your pictures in it in Paint, Paint.net, GIMP, or whatever else you have.

I know you told us not to in your OP, but I think asking what the calendar is for could help a lot in terms of knowing what is needed.