dirt on sensor?

I took this photograph of starlings in the evening light in Shrewsbury yesterday. I was using my compact camera. I noticed a blob near the centre of the picture and as it was spitting with rain assumed it must be a small drop of water. However it will not go away - and I have cleaned the lens.

I have had problems previously with dust on the sensor of a digital SLR ... but with an enclosed compact camera I am not sure how this can happen. But that is what the problem looks like. Though the size of the blog changes dependent on the magnification ... which I am not sure one would expect. Another example tomorrow!