adding an electric range/oven in house with only 100amp main service?
Your panel needs to be reviewed, carefully.

When you do, you'll have no trouble finding 2 spaces. 

It's a quality CH panel, albeit with only 20 spaces.  I'm not counting the top 2 spaces in each row, which collectively are the main breaker (100A).   Good news is, with this panel arrangement, if you shut off the main breaker, everything is cold except those conspicuous large screws. Which makes it more DIY-friendly than most. 

I see seven 240V breakers tying up 14 of 20 spaces.  That means all 120V loads in the entire house are served by six 120V breakers, which is pretty compact.  I don't believe a house can have seven 240V loads.  The usual big four are dryer, A/C, water heater and oven. So I suspect many of these breakers are surplus, particularly since they're off. 

The only conceivable reason for this many 240V breakers is having all-electric heat, e.g. baseboard, and if that's the case, forget about an electric range/oven - you just don't have enough service.

Two of those 240V loads are 120/240 split phase.  The right side middle rows are a 30A breaker, and looks to have the heavier 10 AWG wire, so it looks to be a dryer.  The left side 4th and 5th from the bottom is weird because the white wire is being used as a hot, and the red wire is taped white and used as a neutral (which is illegal to do).  That's not right.  It might be a multi-wire branch circuit or MWBC, serving two 120V circuits, but I doubt it.  

I see a red wire that's taped off, that means there's another black-red-white cable with black and white only being used. That seems weirdly sloppy (why use white for a 240V circuit when you have red) which only worries me more about the quality of work in general. 

Even worse, look at the bottom right breaker.  It's a 60A breaker but that's NOT a 4 AWG wire. It's either 12 AWG or maybe 10 AWG. That needs a 20A or 30A breaker, respectively.  I know exactly what those breakers cost, so no excuse!  SHUT IT OFF NOW.  NEVER turn it back on.  Replace with a 20 or 30A breaker respectively, most hardware stores stock CH220 or CH230.  And if it trips, it's supposed to. 

Other than that, Mrs. Lincoln...

Go through each circuit in the panel, for two reasons.  First, to find any more defects -- after all, I could find two whoppers from a photo.  Second, to understand what you do have, so you can either trim or consolidate and free up 2 breaker spaces.

Don't bother hunting down double-stuff (duplex/tandem) CH breakers.  Yes, they exist, but you really, really need to re-evaluate this panel, given the large number of defects I've seen from one measly photo.  And I think as you do so, you'll free up some space. 

Oven/range is straightforward

You simply need a 50A breaker and 6 AWG copper (or 4 AWG aluminum).  You could go 40A and 8 AWG, but the difference is only a few bucks, and you'll have a wider selection of ovens/ranges if you go 50A.  CH 50A breakers are readily available, not quite as widely stocked as the 20/30s but any big-box should have them.   You cannot reuse the 60A breaker.  

However, cooking on electric kinda sucks, if you're coming from gas.  It's a very annoying learning curve, and a lot of compromises and workarounds. Not recommended.

If you must upgrade the panel

CH is a fine system.  One option is get a larger CH panel.  However, if you replace the panel, you will need to upgrade most of all of your 6-8 120V loads to AFCI or GFCI or both/combo, and that could get costly.  The disadvantage to CH or any 3/4" wide breaker is being smaller, there's less space to cram advanced tech, so they're more expensive or unavailable. 

Don't go cheap. This panel is much better than the Homelite and other shlock the local big-box is shoveling. (You can't go by brand anymore, as good brands like Square D and Eaton have bought up cheapie sub-brands.)  You have to ask for the good stuff.  Get a top-shelf panel from a proper electrical supply. And go really big - bare minimum 42-space, 60-space is not too many.  If the main breaker for such a panel is too large, bypass it - put a 100A breaker in the normal spaces and backfeed it (much like is occurring in this panel).