One way to look at a LimeSDR-USB/LimeSDR-Mini board is as a component of a high quality radio. But it has nearly zero no fronted filtering. If you are seeing images of FM everywhere it is because of Heterodyne mixing which takes one signal and creates two new overlapping signals (f1+f2 and f1-f2) and unfiltered undersampling, which ultimately due to Nyquist will produce aliases everywhere. So you have three options and all of them involve adding an external filter to limit unwanted signals from entering the SDR.
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You could use a bandpass filter to attenuate everything outside the band that you are interested in, this would typically overall give the best results for that band.
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If all the signals you are interested in are below FM use a low pass filter that is lower than FM (anywhere lower than 88 MHz) that will attenuate the FM signals and LTE signals and any other unwanted signals (sources of noise) from entering the SDR.
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And lastly you could use one, or more*, bandstop filters to block unwanted signals from entering the SDR. So an FM bandstop filter (88-108MHz) in series with bandstop for your local LTE frequency band. This would, depending on your local RF environment, probably produce the worst results because there are still many unwanted signals (sources of noise) entering the SDR. *But each filter adds ~3dB of attenuation.
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There is a fourth option that does not involve external filters, which is more complex, and may not always be possible. And that is to carefully adjust the tuned frequency and sample rate to nudge unwanted signals slightly further away. But it is not always possible with two or more unwanted signals moving one away from the frequency that you want to see may move another unwanted signal closer.
But any of the above three filtering options will typically produce much better results than an unfiltered RF frontend, depending on your local RF environment (If you were on an island in the middle of the ocean, adding a filter may not help, in fact it might be detrimental because it would add ~3dB of attenuation).
LimeSDR has a separate board LimeRFE board that has a series of bandpass filters with power amplifiers for HAM, Cellular bands.